Is combining PDFs the same as merging them?
Yes — one operation, two words for it, and this is the page for both. Whichever you call it, the pages of each document are copied into a new one in the order you choose. Nothing else on this site does it differently: there is one tool rather than a “combine” page and a “merge” page saying the same thing in different adjectives.
Does merging reduce the quality?
No. The pages are copied as they are — the same fonts, the same images, the same vector drawings, at the same resolution. Nothing is re-encoded, so a merged document looks exactly like its sources placed end to end.
Can I take only some pages from a file?
Yes. Every document in the list has an optional page range beside it. Write 2-5, or 1-3, 8, and only those pages are taken from that file; leave it empty and the whole document is used.
Will the merged file carry my name or the original titles?
No. The new document is created empty and the pages are copied into it, so no title, author, producer or timestamp comes across from any source. If you want a title on the result, add one in whatever you open it with.
One of my files is refused. Why?
Because it is encrypted and this tool has no field for the original password. The message names the file so you know which one to unlock. Take the password off it with the unlock tool on this site — you will need the password it opens with — and add the copy that produces.
Is there a limit on how many files?
Only your device's memory. Everything happens in this browser tab, so a hundred small documents are fine and a handful of very large scans may not be. There is no server-side limit because there is no server.