Add documentation for all PDF tools

docs/tools/json-to-pdf.md

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+---
+title: JSON to PDF
+description: Reconstruct PDF files from BentoPDF's JSON format. Convert JSON exports back to their original PDF documents.
+---
+
+# JSON to PDF
+
+Reconstruct PDF documents from JSON files that were previously created by BentoPDF's **PDF to JSON** tool. This is a round-trip conversion tool -- it takes the structured JSON representation of a PDF and rebuilds the original document.
+
+::: warning
+This tool only accepts JSON files produced by BentoPDF's PDF to JSON converter. Standard JSON files from APIs, databases, or other tools are not supported.
+:::
+
+## Supported Formats
+
+| Input   | Description                                        |
+| :------ | :------------------------------------------------- |
+| `.json` | JSON files exported by BentoPDF's PDF to JSON tool |
+
+## How It Works
+
+1. Click the upload area or drag and drop one or more JSON files.
+2. The file list shows each selected file with its size.
+3. Click **Convert to PDF**. The tool processes all files using a Web Worker and the CPDF engine.
+4. The output downloads as `jsons-to-pdf.zip` containing one PDF per input JSON file.
+
+The conversion runs in a background Web Worker, so the UI remains responsive even with large files.
+
+## Options
+
+This tool has no configurable options. The JSON structure fully determines the output PDF.
+
+## Output
+
+When converting multiple JSON files, results are delivered as a ZIP archive. Each PDF is named after its source JSON file (e.g., `report.json` becomes `report.pdf`).
+
+## Use Cases
+
+- Restoring PDFs from a JSON-based backup or archival pipeline
+- Round-tripping a PDF through JSON for inspection and then back to PDF
+- Rebuilding documents after programmatic modifications to the JSON structure
+- Verifying that a PDF-to-JSON export captured all document content by converting it back
+
+## Tips
+
+- If you need to convert arbitrary JSON data (like API responses or config files) into a formatted PDF, the [Text to PDF](./txt-to-pdf) tool is a better fit. Paste the JSON as text and it will be rendered with proper formatting.
+- The CPDF WebAssembly engine must be available for this tool to work. Self-hosted instances need the CPDF WASM files configured.
+
+## Related Tools
+
+- [Text to PDF](./txt-to-pdf)
+- [Markdown to PDF](./markdown-to-pdf)
+- [CSV to PDF](./csv-to-pdf)