Are my PDFs uploaded to a server?

No. FileSlim's merge tool uses pdf-lib in your browser via WebAssembly-free JavaScript. Your files never leave your device.

Is there a file size or count limit?

There's no hard limit, but combined size is bounded by available browser memory — typically 500 MB to 1 GB on modern desktops.

Page content, annotations, and most metadata are preserved. Form fields are kept per-page; if duplicate field names exist they'll be renamed.

Last Updated: September 12, 2026

Combine multiple PDF files into one — drag to reorder, merge instantly. Runs in your browser. No upload, no signup.