Why can't I combine PDF files?

You usually can't combine PDF files for one of two reasons. The free Adobe Acrobat Reader only views PDFs, and combining them is a paid Acrobat feature. Or one of the PDFs is password protected, which stops it being merged.

If a file has a password, open it, save a copy without the password, then try again.

For everything else, drop your PDFs into the merger below, drag them into order and download one combined PDF. No account, no watermark.