Add documentation for all PDF tools

docs/tools/edit-metadata.md

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+---
+title: Edit Metadata
+description: View and modify PDF metadata fields including title, author, keywords, dates, and custom properties.
+---
+
+# Edit Metadata
+
+Edit the metadata embedded in a PDF file. The tool pre-populates a form with the document's existing metadata, lets you modify any field, and saves the changes into a new PDF.
+
+## How It Works
+
+1. Upload a PDF file. The tool reads its current metadata and populates the form.
+2. Edit any of the standard fields: Title, Author, Subject, Keywords, Creator, Producer.
+3. Adjust the Creation Date and Modification Date using date-time pickers.
+4. Add custom metadata fields by clicking the add button and entering a key-value pair.
+5. Click the process button to save the modified PDF.
+
+## Features
+
+- Pre-fills all existing metadata from the uploaded PDF
+- Standard fields: Title, Author, Subject, Keywords, Creator, Producer
+- Date-time pickers for Creation Date and Modification Date
+- Custom key-value metadata fields for arbitrary properties
+- Saves changes directly into the PDF's document info dictionary
+
+## Editable Fields
+
+| Field                 | Description                                          |
+| --------------------- | ---------------------------------------------------- |
+| **Title**             | The document title displayed in PDF readers          |
+| **Author**            | The person or organization that created the document |
+| **Subject**           | A brief description of the document's topic          |
+| **Keywords**          | Comma-separated terms for search and categorization  |
+| **Creator**           | The application that originally created the content  |
+| **Producer**          | The application that generated the PDF               |
+| **Creation Date**     | When the document was originally created             |
+| **Modification Date** | When the document was last modified                  |
+| **Custom fields**     | Any additional key-value pairs you define            |
+
+## Use Cases
+
+- Setting a proper title and author before publishing a document
+- Adding keywords to improve searchability in document management systems
+- Updating the modification date to reflect the current revision
+- Adding custom metadata fields like Department, Project ID, or Classification
+- Cleaning up metadata left by the original authoring software
+
+## Tips
+
+- Custom fields are written directly into the PDF's info dictionary. Some PDF readers may not display custom fields, but they are preserved in the file.
+- Leave a field blank to clear it from the metadata. The process button saves whatever is in the form.
+- To view metadata without editing, use [View Metadata](./view-metadata). To remove all metadata entirely, use Remove Metadata.
+
+## Related Tools
+
+- [View Metadata](./view-metadata)
+- [PDF OCG Layers](./pdf-layers)
+- [Compress PDF](./compress-pdf)