Add documentation for all PDF tools

docs/tools/pdf-to-zip.md

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+---
+title: PDFs to ZIP
+description: Package multiple PDF files into a single ZIP archive for easy sharing and storage.
+---
+
+# PDFs to ZIP
+
+Bundle multiple PDF files into a single ZIP archive. This is a straightforward packaging tool -- no conversion, compression, or modification of the PDFs themselves.
+
+## How It Works
+
+1. Upload multiple PDF files using the drop zone.
+2. Review the list of files. Remove any you do not want included.
+3. Click the process button.
+4. A ZIP archive containing all the uploaded PDFs downloads immediately.
+
+## Features
+
+- Accepts any number of PDF files
+- Per-file removal before creating the archive
+- Preserves original file names inside the ZIP
+- No modification of PDF content -- files are packaged as-is
+- Displays file name and size for each uploaded PDF
+
+## Use Cases
+
+- Bundling a set of invoices or receipts for email attachment
+- Packaging project deliverables (multiple PDF reports) for handoff
+- Creating a single download for a collection of forms or templates
+- Archiving a batch of documents into one compressed file
+
+## Tips
+
+- The ZIP file uses the original PDF filenames. If you have files with the same name, rename them before uploading to avoid conflicts.
+- This tool does not compress the PDFs themselves. For file size reduction, run them through Compress PDF first, then package with this tool.
+
+## Related Tools
+
+- [Merge PDF](./merge-pdf)
+- [Split PDF](./split-pdf)
+- [Compress PDF](./compress-pdf)