Alternate & Mix Pages

A normal merge appends whole files one after another. Alternate merge takes page 1 from each file in turn, then page 2 from each, and so on, so the pages of two or more PDFs are interleaved into a single document. If you only need files back to back, use Merge PDF.

Upload the fronts PDF first and the backs PDF second, then click Mix Pages. The output alternates front 1, back 1, front 2, back 2 and so on. If the backs were scanned last page first, flip that file with Reverse Pages before mixing.

This tool interleaves separate files. If one PDF holds all the fronts followed by all the backs, Duplex Collate splits that single file at the midpoint and interleaves the two halves, with an option to reverse the back block.

Interleaving continues until the shorter file runs out, and the remaining pages from the longer file are appended in order at the end. No pages are dropped.

Any number of files from two upward. With three files the output goes A1, B1, C1, A2, B2, C2 and so on, following the order shown in the file list, which you can change by dragging the grip handles.

Bookmarks from each source file are carried into the mixed PDF. Page labels are reset to a plain 1 to N sequence by default; turn on the option to keep original page labels if you want each file's own labels, which can produce duplicates such as two pages both labeled 1.

If a file is encrypted you're asked for its password when it loads, and the decrypted copy is used for mixing. The output isn't encrypted, so use Protect PDF afterward if it needs a password again.

No. The files are read in your browser and interleaved by a WebAssembly build of cpdf running in a background worker on your device, and the finished alternated-mixed.pdf is saved straight from the browser.