Merge PDF

Bookmarks inside your original files are not carried across, because the merged document is built from copied pages and the original catalogue stays behind. To make up for it, this tool writes a fresh bookmark for each file you added, pointing at that file first page, so the result still opens with a usable contents list. You can turn that off in Advanced options.

Links to a web address keep working. Links that jump to another page of the same document usually do not, because the copy does not remap those targets to their new positions in the merged file. If a document is full of cross references, merging is the wrong tool for it. Keep it separate, or export a fresh PDF from whatever produced it.

It interleaves them. Scanners without a duplex unit make you scan all the fronts, flip the stack, then scan all the backs, leaving two files that need weaving together rather than joining end to end. With exactly two files loaded, the option appears in Advanced options. If the backs came out reversed, reverse that file first.

Printing double sided. If a file ends on an odd page, the next file starts on the back of that sheet, which is wrong for anything you plan to staple or bind. The option in Advanced options adds one blank page where needed, so each document in the stack begins on a fresh right hand sheet.

No. A digital signature covers the exact bytes of one file, and merging writes a new file, so the signature stops validating. That is the signature doing its job rather than a fault in the tool. If you need a signature over the whole thing, merge first and sign the combined document afterwards.

Not directly. An encrypted file cannot be read here at all, so nothing can be copied out of it. Open it in a reader that has the password, save an unlocked copy, and merge that copy instead. The tool tells you which file was the problem rather than failing silently partway through.

There is no fixed limit, but everything is held in your device memory, so a phone runs out sooner than a laptop. Page thumbnails are drawn one at a time with a running count, so a long file looks busy rather than frozen. If a merge of very large scans stalls, try it on a desktop or in smaller batches.

No. Each file is read into memory in this page, and the merged document is written there too. There is no upload, no queue and no server copy, which you can confirm in the network tab: choose your files and watch nothing happen. Closing the tab discards everything.