Add documentation for all PDF tools

docs/tools/excel-to-pdf.md

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+---
+title: Excel to PDF
+description: Convert Excel spreadsheets (XLS, XLSX), ODS, and CSV files to PDF with formatting preserved.
+---
+
+# Excel to PDF
+
+Convert spreadsheet files to PDF. The tool handles modern Excel files, legacy XLS format, OpenDocument Spreadsheets, and even CSV -- all rendered through a browser-based LibreOffice engine that preserves cell formatting, formulas (as computed values), charts, and multi-sheet layouts.
+
+## Supported Formats
+
+| Format                   | Extensions |
+| :----------------------- | :--------- |
+| Excel (modern)           | `.xlsx`    |
+| Excel (legacy)           | `.xls`     |
+| OpenDocument Spreadsheet | `.ods`     |
+| CSV                      | `.csv`     |
+
+## How It Works
+
+1. Click the upload area or drag and drop your spreadsheet files.
+2. Review the file list. Add more files or remove unwanted ones.
+3. Click **Convert to PDF**. The LibreOffice engine initializes on first use, then processes each file.
+4. A single file downloads directly as a PDF. Multiple files are delivered as `excel-converted.zip`.
+
+## Options
+
+This tool has no additional configuration. The LibreOffice engine determines page layout, scaling, and print area based on the spreadsheet's built-in settings.
+
+## Output
+
+| Input Count | Output                                                          |
+| :---------- | :-------------------------------------------------------------- |
+| 1 file      | Single PDF download (original filename with `.pdf` extension)   |
+| 2+ files    | ZIP archive (`excel-converted.zip`) containing one PDF per file |
+
+## Use Cases
+
+- Converting financial reports or budgets from Excel to PDF for distribution
+- Creating print-ready PDFs from inventory or product catalog spreadsheets
+- Sharing data analysis results with stakeholders who do not have Excel installed
+- Archiving quarterly reports in a non-editable format
+- Converting ODS files from LibreOffice Calc to PDF
+
+## Tips
+
+- Charts embedded in the spreadsheet are rendered in the PDF. Make sure they look correct in the source file before converting.
+- If your spreadsheet has multiple sheets, all sheets are included in the PDF output.
+- For simple CSV data without formatting, the [CSV to PDF](./csv-to-pdf) tool provides a more lightweight conversion. Use Excel to PDF when you need formatting, charts, or multiple sheets preserved.
+
+## Related Tools
+
+- [CSV to PDF](./csv-to-pdf)
+- [Word to PDF](./word-to-pdf)
+- [PowerPoint to PDF](./powerpoint-to-pdf)