How PDF merging works in the browser
This tool uses the open-source pdf-lib library to read each PDF file you add, extract every page, and copy them into a new combined document. Text, images, vector graphics, and annotations attached to individual pages all carry over to the merged output.
Because pdf-lib runs entirely in JavaScript, the merge happens in your browser's memory. There's no server involved. Your documents are never transmitted over the internet, which makes this safe for confidential or sensitive files.
What a merge cannot carry across
A PDF stores some things on individual pages and others on the document as a whole. Page-level content copies cleanly. Two document-level structures do not: the outline tree that produces bookmarks, and the AcroForm dictionary that makes form fields interactive.
When those exist in your input files, copying pages into a fresh document leaves them behind — filled-in form values would become flat, non-interactive content. Rather than let that happen silently, the tool inspects each file first and shows a warning alongside the result. If you need to preserve a filled form, flatten it in your PDF reader before merging.
When to use PDF merging
- Combining scanned documents into a single file for archiving
- Assembling a report from separate chapters or sections
- Merging signed contracts with appendices
- Creating a single submission file from multiple forms
File order and page sequence
The merged PDF follows the order you arrange your files in. Use the up and down controls to rearrange before merging. All pages from each file are included in sequence — there's no option to select individual pages during a merge. If you need to extract specific pages first, use the Split PDF tool.
The tool handles up to 20 files at a time, each up to 100MB. Processing time depends on the total page count and your device's available memory.