Add documentation for all PDF tools

docs/tools/combine-single-page.md

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+---
+title: Combine to Single Page
+description: Stitch all pages of a PDF into one continuous vertical or horizontal scroll.
+---
+
+# Combine to Single Page
+
+Merge every page of a PDF into a single, long page. Pages are stitched together vertically (like a scroll) or horizontally (side by side), producing one continuous page in the output.
+
+## How It Works
+
+1. Upload a PDF file.
+2. Select the layout direction: **Vertical** (pages stacked top to bottom) or **Horizontal** (pages placed side by side).
+3. Set the spacing between pages in points.
+4. Choose a background color for the gaps between pages.
+5. Optionally enable separators (thin lines between pages) and configure their thickness and color.
+6. Click the process button. The output is a single-page PDF.
+
+## Features
+
+- Vertical or horizontal page stitching
+- Configurable spacing between pages
+- Background color picker for the gap areas
+- Optional separator lines with adjustable thickness and color
+- Renders each original page at full resolution onto the combined canvas
+
+## Options
+
+| Option                  | Description                                     |
+| ----------------------- | ----------------------------------------------- |
+| **Orientation**         | Vertical (stacked) or Horizontal (side by side) |
+| **Page spacing**        | Gap between pages in points                     |
+| **Background color**    | Color of the area between pages                 |
+| **Add separator**       | Toggle thin lines between pages                 |
+| **Separator thickness** | Line thickness in points                        |
+| **Separator color**     | Color of the separator lines                    |
+
+## Use Cases
+
+- Creating a single long image from a multi-page wireframe or design mockup
+- Generating a continuous scrollable view of a document for web embedding
+- Stitching together a multi-page comic or storyboard into one strip
+- Producing a panoramic view of sequential pages for review
+
+## Tips
+
+- Vertical orientation works best for documents with portrait pages. Horizontal is better for landscape-oriented content.
+- Large documents with many pages will produce a very tall or wide output. Some PDF viewers may struggle with extremely large single pages.
+- Adding separators with a contrasting color makes it easy to see where one original page ends and the next begins.
+
+## Related Tools
+
+- [N-Up PDF](./n-up-pdf)
+- [Merge PDF](./merge-pdf)
+- [Divide Pages](./divide-pages)