Overlay PDF tool (#4620)

# Description of Changes

- Added the OverlayPDF tool

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

frontend/public/locales/en-GB/translation.json

@@ -598,11 +598,6 @@
       "title": "Redact",
       "desc": "Redacts (blacks out) a PDF based on selected text, drawn shapes and/or selected page(s)"
     },
-    "overlayPdfs": {
-      "tags": "overlay,combine,stack",
-      "title": "Overlay PDFs",
-      "desc": "Overlays PDFs on-top of another PDF"
-    },
     "splitBySections": {
       "tags": "split,sections,divide",
       "title": "Split PDF by Sections",
@@ -2550,11 +2545,15 @@
   "overlay-pdfs": {
     "tags": "Overlay",
     "header": "Overlay PDF Files",
+    "title": "Overlay PDFs",
+    "desc": "Overlay one PDF on top of another",
     "baseFile": {
       "label": "Select Base PDF File"
     },
     "overlayFiles": {
-      "label": "Select Overlay PDF Files"
+      "label": "Select Overlay PDF Files",
+      "placeholder": "Choose PDF(s)...",
+      "addMore": "Add more PDFs..."
     },
     "mode": {
       "label": "Select Overlay Mode",
@@ -2564,14 +2563,49 @@
     },
     "counts": {
       "label": "Overlay Counts (for Fixed Repeat Mode)",
-      "placeholder": "Enter comma-separated counts (e.g., 2,3,1)"
+      "placeholder": "Enter comma-separated counts (e.g., 2,3,1)",
+      "item": "Count for file"
     },
     "position": {
       "label": "Select Overlay Position",
       "foreground": "Foreground",
       "background": "Background"
     },
-    "submit": "Submit"
+    "submit": "Submit",
+    "settings": {
+      "title": "Settings"
+    },
+    "results": {
+      "title": "Overlay Results"
+    },
+    "tooltip": {
+      "header": {
+        "title": "Overlay PDFs Overview"
+      },
+      "description": {
+        "title": "Description",
+        "text": "Combine a base PDF with one or more overlay PDFs. Overlays can be applied page-by-page in different modes and placed in the foreground or background."
+      },
+      "mode": {
+        "title": "Overlay Mode",
+        "text": "Choose how to distribute overlay pages across the base PDF pages.",
+        "sequential": "Sequential Overlay: Use pages from the first overlay PDF until it ends, then move to the next.",
+        "interleaved": "Interleaved Overlay: Take one page from each overlay in turn.",
+        "fixedRepeat": "Fixed Repeat Overlay: Take a set number of pages from each overlay before moving to the next. Use Counts to set the numbers."
+      },
+      "position": {
+        "title": "Overlay Position",
+        "text": "Foreground places the overlay on top of the page. Background places it behind."
+      },
+      "overlayFiles": {
+        "title": "Overlay Files",
+        "text": "Select one or more PDFs to overlay on the base. The order of these files affects how pages are applied in Sequential and Fixed Repeat modes."
+      },
+      "counts": {
+        "title": "Counts (Fixed Repeat only)",
+        "text": "Provide a positive number for each overlay file showing how many pages to take before moving to the next. Required when mode is Fixed Repeat."
+      }
+    }
   },
   "split-by-sections": {
     "tags": "Section Split, Divide, Customize,Customise",

frontend/public/locales/en-US/translation.json

@@ -1521,11 +1521,15 @@
   "overlay-pdfs": {
     "tags": "Overlay",
     "header": "Overlay PDF Files",
+    "title": "Overlay PDFs",
+    "desc": "Overlay one PDF on top of another",
     "baseFile": {
       "label": "Select Base PDF File"
     },
     "overlayFiles": {
-      "label": "Select Overlay PDF Files"
+      "label": "Select Overlay PDF Files",
+      "placeholder": "Choose PDF(s)...",
+      "addMore": "Add more PDFs..."
     },
     "mode": {
       "label": "Select Overlay Mode",
@@ -1535,14 +1539,49 @@
     },
     "counts": {
       "label": "Overlay Counts (for Fixed Repeat Mode)",
-      "placeholder": "Enter comma-separated counts (e.g., 2,3,1)"
+      "placeholder": "Enter comma-separated counts (e.g., 2,3,1)",
+      "item": "Count for file"
     },
     "position": {
       "label": "Select Overlay Position",
       "foreground": "Foreground",
       "background": "Background"
     },
-    "submit": "Submit"
+    "submit": "Submit",
+    "settings": {
+      "title": "Settings"
+    },
+    "results": {
+      "title": "Overlay Results"
+    },
+    "tooltip": {
+      "header": {
+        "title": "Overlay PDFs Overview"
+      },
+      "description": {
+        "title": "Description",
+        "text": "Combine a base PDF with one or more overlay PDFs. Overlays can be applied page-by-page in different modes and placed in the foreground or background."
+      },
+      "mode": {
+        "title": "Overlay Mode",
+        "text": "Choose how to distribute overlay pages across the base PDF pages.",
+        "sequential": "Sequential Overlay: Use pages from the first overlay PDF until it ends, then move to the next.",
+        "interleaved": "Interleaved Overlay: Take one page from each overlay in turn.",
+        "fixedRepeat": "Fixed Repeat Overlay: Take a set number of pages from each overlay before moving to the next. Use Counts to set the numbers."
+      },
+      "position": {
+        "title": "Overlay Position",
+        "text": "Foreground places the overlay on top of the page. Background places it behind."
+      },
+      "overlayFiles": {
+        "title": "Overlay Files",
+        "text": "Select one or more PDFs to overlay on the base. The order of these files affects how pages are applied in Sequential and Fixed Repeat modes."
+      },
+      "counts": {
+        "title": "Counts (Fixed Repeat only)",
+        "text": "Provide a positive number for each overlay file showing how many pages to take before moving to the next. Required when mode is Fixed Repeat."
+      }
+    }
   },
   "split-by-sections": {
     "tags": "Section Split, Divide, Customize",

frontend/src/components/FileManager.tsx

@@ -125,6 +125,7 @@ const FileManager: React.FC<FileManagerProps> = ({ selectedTool }) => {
       radius="md"
       className="overflow-hidden p-0"
       withCloseButton={false}
+      zIndex={1100}
       styles={{
         content: {
           position: 'relative',

frontend/src/components/shared/FilePickerModal.tsx

@@ -125,6 +125,7 @@ const FilePickerModal = ({
       title={t("fileUpload.selectFromStorage", "Select Files from Storage")}
       size="lg"
       scrollAreaComponent={ScrollArea.Autosize}
+      zIndex={1100}
     >
       <Stack gap="md">
         {storedFiles.length === 0 ? (

frontend/src/components/tools/overlayPdfs/OverlayPdfsSettings.module.css

@@ -0,0 +1,50 @@
+.fileListContainer {
+  max-height: 16.25rem;
+  overflow-y: auto;
+  overflow-x: hidden;
+  width: 100%;
+}
+
+.fileItem {
+  border: 1px solid var(--mantine-color-gray-3);
+  border-radius: var(--mantine-radius-sm);
+  align-items: center;
+  width: 100%;
+}
+
+.fileNameContainer {
+  flex: 1;
+  min-width: 0;
+}
+
+.fileName {
+  font-size: var(--mantine-font-size-sm);
+  font-weight: 400;
+  line-height: 1.2;
+  display: -webkit-box;
+  -webkit-line-clamp: 1;
+  line-clamp: 1;
+  -webkit-box-orient: vertical;
+  overflow: hidden;
+  white-space: normal;
+  word-break: break-word;
+}
+
+.fileSize {
+  flex-shrink: 0;
+}
+
+.removeButton {
+  flex-shrink: 0;
+}
+
+.countLabel {
+  width: 140px;
+  flex-shrink: 0;
+}
+
+.fileGroup {
+  flex: 1;
+  min-width: 0;
+  align-items: center;
+}

frontend/src/components/tools/overlayPdfs/OverlayPdfsSettings.tsx

@@ -0,0 +1,178 @@
+import { Stack, Text, Group, Select, SegmentedControl, NumberInput, Button, ActionIcon, Divider } from '@mantine/core';
+import { useTranslation } from 'react-i18next';
+import { type OverlayPdfsParameters, type OverlayMode } from '../../../hooks/tools/overlayPdfs/useOverlayPdfsParameters';
+import LocalIcon from '../../shared/LocalIcon';
+import { useFilesModalContext } from '../../../contexts/FilesModalContext';
+import styles from './OverlayPdfsSettings.module.css';
+
+interface OverlayPdfsSettingsProps {
+  parameters: OverlayPdfsParameters;
+  onParameterChange: <K extends keyof OverlayPdfsParameters>(key: K, value: OverlayPdfsParameters[K]) => void;
+  disabled?: boolean;
+}
+
+export default function OverlayPdfsSettings({ parameters, onParameterChange, disabled = false }: OverlayPdfsSettingsProps) {
+  const { t } = useTranslation();
+  const { openFilesModal } = useFilesModalContext();
+
+  const handleOverlayFilesChange = (files: File[]) => {
+    onParameterChange('overlayFiles', files);
+    // Reset counts to match number of files if in FixedRepeatOverlay
+    if (parameters.overlayMode === 'FixedRepeatOverlay') {
+      const nextCounts = files.map((_, i) => parameters.counts[i] && parameters.counts[i] > 0 ? parameters.counts[i] : 1);
+      onParameterChange('counts', nextCounts);
+    }
+  };
+
+  const handleModeChange = (mode: OverlayMode) => {
+    onParameterChange('overlayMode', mode);
+    if (mode !== 'FixedRepeatOverlay') {
+      onParameterChange('counts', []);
+    } else if (parameters.overlayFiles?.length > 0) {
+      onParameterChange('counts', parameters.overlayFiles.map((_, i) => parameters.counts[i] && parameters.counts[i] > 0 ? parameters.counts[i] : 1));
+    }
+  };
+
+  const handleOpenOverlayFilesModal = () => {
+    if (disabled) return;
+    openFilesModal({
+      customHandler: (files: File[]) => {
+        handleOverlayFilesChange([...(parameters.overlayFiles || []), ...files]);
+      }
+    });
+  };
+
+  return (
+    <Stack gap="md">
+
+      <Stack gap="xs">
+        <Text size="sm" fw={500}>{t('overlay-pdfs.mode.label', 'Overlay Mode')}</Text>
+        <Select
+          data={[
+            { value: 'SequentialOverlay', label: t('overlay-pdfs.mode.sequential', 'Sequential Overlay') },
+            { value: 'InterleavedOverlay', label: t('overlay-pdfs.mode.interleaved', 'Interleaved Overlay') },
+            { value: 'FixedRepeatOverlay', label: t('overlay-pdfs.mode.fixedRepeat', 'Fixed Repeat Overlay') },
+          ]}
+          value={parameters.overlayMode}
+          onChange={(v) => handleModeChange((v || 'SequentialOverlay') as OverlayMode)}
+          disabled={disabled}
+        />
+      </Stack>
+
+      <Divider />
+
+      <Stack gap="xs">
+        <Text size="sm" fw={500}>{t('overlay-pdfs.position.label', 'Overlay Position')}</Text>
+        <SegmentedControl
+          value={String(parameters.overlayPosition)}
+          onChange={(v) => onParameterChange('overlayPosition', (v === '1' ? 1 : 0) as 0 | 1)}
+          data={[
+            { label: t('overlay-pdfs.position.foreground', 'Foreground'), value: '0' },
+            { label: t('overlay-pdfs.position.background', 'Background'), value: '1' },
+          ]}
+          disabled={disabled}
+        />
+      </Stack>
+
+      {parameters.overlayMode === 'FixedRepeatOverlay' && (
+        <>
+          <Divider />
+          <Stack gap="xs">
+            <Text size="sm" fw={500}>{t('overlay-pdfs.counts.label', 'Overlay Counts')}</Text>
+            {parameters.overlayFiles?.length > 0 ? (
+              <Stack gap="xs">
+                {parameters.overlayFiles.map((_, index) => (
+                  <Group key={index} gap="xs" wrap="nowrap">
+                    <Text size="sm" className={styles.countLabel}>
+                      {t('overlay-pdfs.counts.item', 'Count for file')} {index + 1}
+                    </Text>
+                    <NumberInput
+                      min={1}
+                      step={1}
+                      value={parameters.counts[index] ?? 1}
+                      onChange={(value) => {
+                        const next = [...(parameters.counts || [])];
+                        next[index] = Number(value) || 1;
+                        onParameterChange('counts', next);
+                      }}
+                      disabled={disabled}
+                    />
+                  </Group>
+                ))}
+              </Stack>
+            ) : (
+              <Text size="sm" c="dimmed">
+                {t('overlay-pdfs.counts.noFiles', 'Add overlay files to configure counts')}
+              </Text>
+            )}
+          </Stack>
+        </>
+      )}
+
+      <Divider />
+
+      <Stack gap="xs">
+        <Text size="sm" fw={500}>{t('overlay-pdfs.overlayFiles.label', 'Overlay Files')}</Text>
+        <Button
+          size="xs"
+          color="blue"
+          onClick={handleOpenOverlayFilesModal}
+          disabled={disabled}
+          leftSection={<LocalIcon icon="add" width="14" height="14" />}
+          fullWidth
+        >
+          {parameters.overlayFiles?.length > 0
+            ? t('overlay-pdfs.overlayFiles.addMore', 'Add more PDFs...')
+            : t('overlay-pdfs.overlayFiles.placeholder', 'Choose PDF(s)...')}
+        </Button>
+
+        {parameters.overlayFiles?.length > 0 && (() => {
+          return (
+            <div className={styles.fileListContainer}>
+              <Stack gap="xs">
+                {parameters.overlayFiles.map((file, index) => (
+                  <Group
+                    key={index}
+                    justify="space-between"
+                    p="xs"
+                    className={styles.fileItem}
+                  >
+                    <Group gap="xs" className={styles.fileGroup}>
+                      <div className={styles.fileNameContainer}>
+                        <div
+                          className={styles.fileName}
+                          title={file.name}
+                        >
+                          {file.name}
+                        </div>
+                      </div>
+                      <Text size="xs" c="dimmed" className={styles.fileSize}>
+                        ({(file.size / 1024).toFixed(1)} KB)
+                      </Text>
+                    </Group>
+                    <ActionIcon
+                      size="sm"
+                      variant="subtle"
+                      color="red"
+                      className={styles.removeButton}
+                      onClick={() => {
+                        const next = (parameters.overlayFiles || []).filter((_, i) => i !== index);
+                        handleOverlayFilesChange(next);
+                      }}
+                      disabled={disabled}
+                    >
+                      <LocalIcon icon="close-rounded" width="14" height="14" />
+                    </ActionIcon>
+                  </Group>
+                ))}
+              </Stack>
+            </div>
+          );
+        })()}
+      </Stack>
+
+    </Stack>
+  );
+}
+
+

frontend/src/components/tooltips/useOverlayPdfsTips.ts

@@ -0,0 +1,56 @@
+import { useTranslation } from 'react-i18next';
+import { TooltipContent } from '../../types/tips';
+
+export const useOverlayPdfsTips = (): TooltipContent => {
+  const { t } = useTranslation();
+
+  return {
+    header: {
+      title: t('overlay-pdfs.tooltip.header.title', 'Overlay PDFs Overview')
+    },
+    tips: [
+      {
+        title: t('overlay-pdfs.tooltip.description.title', 'Description'),
+        description: t(
+          'overlay-pdfs.tooltip.description.text',
+          'Combine a base PDF with one or more overlay PDFs. Overlays can be applied page-by-page in different modes and placed in the foreground or background.'
+        )
+      },
+      {
+        title: t('overlay-pdfs.tooltip.mode.title', 'Overlay Mode'),
+        description: t(
+          'overlay-pdfs.tooltip.mode.text',
+          'Choose how to distribute overlay pages across the base PDF pages.'
+        ),
+        bullets: [
+          t('overlay-pdfs.tooltip.mode.sequential', 'Sequential Overlay: Use pages from the first overlay PDF until it ends, then move to the next.'),
+          t('overlay-pdfs.tooltip.mode.interleaved', 'Interleaved Overlay: Take one page from each overlay in turn.'),
+          t('overlay-pdfs.tooltip.mode.fixedRepeat', 'Fixed Repeat Overlay: Take a set number of pages from each overlay before moving to the next. Use Counts to set the numbers.')
+        ]
+      },
+      {
+        title: t('overlay-pdfs.tooltip.position.title', 'Overlay Position'),
+        description: t(
+          'overlay-pdfs.tooltip.position.text',
+          'Foreground places the overlay on top of the page. Background places it behind.'
+        )
+      },
+      {
+        title: t('overlay-pdfs.tooltip.overlayFiles.title', 'Overlay Files'),
+        description: t(
+          'overlay-pdfs.tooltip.overlayFiles.text',
+          'Select one or more PDFs to overlay on the base. The order of these files affects how pages are applied in Sequential and Fixed Repeat modes.'
+        )
+      },
+      {
+        title: t('overlay-pdfs.tooltip.counts.title', 'Counts (Fixed Repeat only)'),
+        description: t(
+          'overlay-pdfs.tooltip.counts.text',
+          'Provide a positive number for each overlay file showing how many pages to take before moving to the next. Required when mode is Fixed Repeat.'
+        )
+      }
+    ]
+  };
+};
+
+

frontend/src/data/useTranslatedToolRegistry.tsx

@@ -66,6 +66,10 @@ import { extractImagesOperationConfig } from "../hooks/tools/extractImages/useEx
 import { replaceColorOperationConfig } from "../hooks/tools/replaceColor/useReplaceColorOperation";
 import { removePagesOperationConfig } from "../hooks/tools/removePages/useRemovePagesOperation";
 import { removeBlanksOperationConfig } from "../hooks/tools/removeBlanks/useRemoveBlanksOperation";
+import { overlayPdfsOperationConfig } from "../hooks/tools/overlayPdfs/useOverlayPdfsOperation";
+import { adjustPageScaleOperationConfig } from "../hooks/tools/adjustPageScale/useAdjustPageScaleOperation";
+import { scannerImageSplitOperationConfig } from "../hooks/tools/scannerImageSplit/useScannerImageSplitOperation";
+import { addPageNumbersOperationConfig } from "../components/tools/addPageNumbers/useAddPageNumbersOperation";
 import CompressSettings from "../components/tools/compress/CompressSettings";
 import AddPasswordSettings from "../components/tools/addPassword/AddPasswordSettings";
 import RemovePasswordSettings from "../components/tools/removePassword/RemovePasswordSettings";
@@ -81,16 +85,14 @@ import Redact from "../tools/Redact";
 import AdjustPageScale from "../tools/AdjustPageScale";
 import ReplaceColor from "../tools/ReplaceColor";
 import ScannerImageSplit from "../tools/ScannerImageSplit";
+import OverlayPdfs from "../tools/OverlayPdfs";
 import { ToolId } from "../types/toolId";
 import MergeSettings from '../components/tools/merge/MergeSettings';
-import { adjustPageScaleOperationConfig } from "../hooks/tools/adjustPageScale/useAdjustPageScaleOperation";
-import { scannerImageSplitOperationConfig } from "../hooks/tools/scannerImageSplit/useScannerImageSplitOperation";
 import AdjustPageScaleSettings from "../components/tools/adjustPageScale/AdjustPageScaleSettings";
 import ScannerImageSplitSettings from "../components/tools/scannerImageSplit/ScannerImageSplitSettings";
 import ChangeMetadataSingleStep from "../components/tools/changeMetadata/ChangeMetadataSingleStep";
 import SignSettings from "../components/tools/sign/SignSettings";
 import AddPageNumbers from "../tools/AddPageNumbers";
-import { addPageNumbersOperationConfig } from "../components/tools/addPageNumbers/useAddPageNumbersOperation";
 import RemoveAnnotations from "../tools/RemoveAnnotations";
 import PageLayoutSettings from "../components/tools/pageLayout/PageLayoutSettings";
 import ExtractImages from "../tools/ExtractImages";
@@ -105,6 +107,7 @@ import AddAttachmentsSettings from "../components/tools/addAttachments/AddAttach
 import RemovePagesSettings from "../components/tools/removePages/RemovePagesSettings";
 import RemoveBlanksSettings from "../components/tools/removeBlanks/RemoveBlanksSettings";
 import AddPageNumbersAutomationSettings from "../components/tools/addPageNumbers/AddPageNumbersAutomationSettings";
+import OverlayPdfsSettings from "../components/tools/overlayPdfs/OverlayPdfsSettings";
 
 const showPlaceholderTools = true; // Show all tools; grey out unavailable ones in UI
 
@@ -704,13 +707,14 @@ export function useFlatToolRegistry(): ToolRegistry {
       },
       overlayPdfs: {
         icon: <LocalIcon icon="layers-rounded" width="1.5rem" height="1.5rem" />,
-        name: t("home.overlayPdfs.title", "Overlay PDFs"),
+        name: t("home.overlay-pdfs.title", "Overlay PDFs"),
-        component: null,
+        component: OverlayPdfs,
-        description: t("home.overlayPdfs.desc", "Overlay one PDF on top of another"),
+        description: t("home.overlay-pdfs.desc", "Overlay one PDF on top of another"),
         categoryId: ToolCategoryId.ADVANCED_TOOLS,
         subcategoryId: SubcategoryId.ADVANCED_FORMATTING,
-        synonyms: getSynonyms(t, "overlayPdfs"),
+        operationConfig: overlayPdfsOperationConfig,
-        automationSettings: null
+        synonyms: getSynonyms(t, "overlay-pdfs"),
+        automationSettings: OverlayPdfsSettings
       },
       replaceColor: {
         icon: <LocalIcon icon="format-color-fill-rounded" width="1.5rem" height="1.5rem" />,

frontend/src/hooks/tools/overlayPdfs/useOverlayPdfsOperation.ts

@@ -0,0 +1,46 @@
+import { useTranslation } from 'react-i18next';
+import { useToolOperation, ToolType, type ToolOperationConfig } from '../shared/useToolOperation';
+import { createStandardErrorHandler } from '../../../utils/toolErrorHandler';
+import { type OverlayPdfsParameters } from './useOverlayPdfsParameters';
+
+const buildFormData = (parameters: OverlayPdfsParameters, file: File): FormData => {
+  const formData = new FormData();
+  formData.append('fileInput', file);
+
+  // Overlay files
+  for (const overlay of parameters.overlayFiles || []) {
+    formData.append('overlayFiles', overlay);
+  }
+
+  // Mode and position
+  formData.append('overlayMode', parameters.overlayMode);
+  formData.append('overlayPosition', String(parameters.overlayPosition));
+
+  // Counts (only relevant for FixedRepeatOverlay, server accepts repeated 'counts' fields)
+  if (parameters.overlayMode === 'FixedRepeatOverlay') {
+    for (const count of parameters.counts || []) {
+      formData.append('counts', String(count));
+    }
+  }
+
+  return formData;
+};
+
+export const overlayPdfsOperationConfig: ToolOperationConfig<OverlayPdfsParameters> = {
+  toolType: ToolType.singleFile,
+  buildFormData,
+  operationType: 'overlayPdfs',
+  endpoint: '/api/v1/general/overlay-pdfs'
+};
+
+export const useOverlayPdfsOperation = () => {
+  const { t } = useTranslation();
+  return useToolOperation<OverlayPdfsParameters>({
+    ...overlayPdfsOperationConfig,
+    getErrorMessage: createStandardErrorHandler(
+      t('overlay-pdfs.error.failed', 'An error occurred while overlaying PDFs.')
+    ),
+  });
+};
+
+

frontend/src/hooks/tools/overlayPdfs/useOverlayPdfsParameters.ts

@@ -0,0 +1,37 @@
+import { BaseParameters } from '../../../types/parameters';
+import { useBaseParameters, type BaseParametersHook } from '../shared/useBaseParameters';
+
+export type OverlayMode = 'SequentialOverlay' | 'InterleavedOverlay' | 'FixedRepeatOverlay';
+
+export interface OverlayPdfsParameters extends BaseParameters {
+  overlayFiles: File[];
+  overlayMode: OverlayMode;
+  overlayPosition: 0 | 1;
+  counts: number[];
+}
+
+export const defaultParameters: OverlayPdfsParameters = {
+  overlayFiles: [],
+  overlayMode: 'SequentialOverlay',
+  overlayPosition: 0,
+  counts: []
+};
+
+export type OverlayPdfsParametersHook = BaseParametersHook<OverlayPdfsParameters>;
+
+export const useOverlayPdfsParameters = (): OverlayPdfsParametersHook => {
+  return useBaseParameters<OverlayPdfsParameters>({
+    defaultParameters,
+    endpointName: 'overlay-pdfs',
+    validateFn: (params) => {
+      if (!params.overlayFiles || params.overlayFiles.length === 0) return false;
+      if (params.overlayMode === 'FixedRepeatOverlay') {
+        if (!params.counts || params.counts.length !== params.overlayFiles.length) return false;
+        if (params.counts.some((c) => !Number.isFinite(c) || c <= 0)) return false;
+      }
+      return true;
+    },
+  });
+};
+
+

frontend/src/tools/OverlayPdfs.tsx

@@ -0,0 +1,60 @@
+import { useTranslation } from 'react-i18next';
+import { createToolFlow } from '../components/tools/shared/createToolFlow';
+import { useBaseTool } from '../hooks/tools/shared/useBaseTool';
+import { BaseToolProps, ToolComponent } from '../types/tool';
+import OverlayPdfsSettings from '../components/tools/overlayPdfs/OverlayPdfsSettings';
+import { useOverlayPdfsParameters } from '../hooks/tools/overlayPdfs/useOverlayPdfsParameters';
+import { useOverlayPdfsOperation } from '../hooks/tools/overlayPdfs/useOverlayPdfsOperation';
+import { useOverlayPdfsTips } from '../components/tooltips/useOverlayPdfsTips';
+
+const OverlayPdfs = (props: BaseToolProps) => {
+  const { t } = useTranslation();
+
+  const base = useBaseTool(
+    'overlay-pdfs',
+    useOverlayPdfsParameters,
+    useOverlayPdfsOperation,
+    props
+  );
+  const overlayTips = useOverlayPdfsTips();
+
+  return createToolFlow({
+    files: {
+      selectedFiles: base.selectedFiles,
+      isCollapsed: base.hasResults,
+    },
+    steps: [
+      {
+        title: t('overlay-pdfs.settings.title', 'Settings'),
+        isCollapsed: base.settingsCollapsed,
+        onCollapsedClick: base.settingsCollapsed ? base.handleSettingsReset : undefined,
+        tooltip: overlayTips,
+        content: (
+          <OverlayPdfsSettings
+            parameters={base.params.parameters}
+            onParameterChange={base.params.updateParameter}
+            disabled={base.endpointLoading}
+          />
+        ),
+      },
+    ],
+    executeButton: {
+      text: t('overlay-pdfs.submit', 'Overlay and Review'),
+      isVisible: !base.hasResults,
+      loadingText: t('loading'),
+      onClick: base.handleExecute,
+      disabled: !base.params.validateParameters() || !base.hasFiles || !base.endpointEnabled,
+    },
+    review: {
+      isVisible: base.hasResults,
+      operation: base.operation,
+      title: t('overlay-pdfs.results.title', 'Overlay Results'),
+      onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
+    },
+  });
+};
+
+export default OverlayPdfs as ToolComponent;
+
+