Merge PDF Files

How it works

A PDF is not a stream of pages. It is a graph of numbered objects — page trees, fonts, images, content streams — that reference one another, plus a table at the end saying where each object lives in the file.

Merging correctly means walking that graph. For each source document, every page object is copied into the new document along with everything it depends on, and all the internal references are renumbered so they point at the right objects in their new home. Two documents that both call their font "object 12" cannot simply be concatenated; one of them has to be renumbered throughout.

This is why merging is lossless. Nothing is interpreted, rendered, or re-compressed — the bytes of a page's content stream and the bytes of an embedded JPEG arrive in the new document unchanged. A merged page is the same page.

It is also why the result is usually slightly smaller than the sum of its inputs. Each source file carried its own cross-reference table, document catalog, and trailer, and the merged file needs only one set.

The page count for each file is read as soon as you add it rather than when you press Merge. That ordering is deliberate: it puts encryption and corruption errors in front of you while you are still arranging the list, instead of after a wait.

When you'd use this

Applications and submissions, where a portal wants one file and you have a cover letter, a CV, and a certificate. This is the most common reason by a wide margin.

Scanned documents that arrived in pieces, either because the feeder jammed or because the scanner splits at a page limit.

Reports and packs assembled from separate sources — a summary from one tool, a chart export from another, an appendix from a third.

Invoices, receipts, and statements being combined for an accountant or a claim, which is exactly the category of document worth not uploading to a free website.

What happens to your documents

This section used to argue that the merge happened in your browser and that there was therefore no server to trust. That was true once and is not now — the processing libraries moved to the server, and this page did not move with them. Correcting it plainly is better than deleting it, because the argument it made is still the right argument; it simply applies to us as much as to anyone.

The documents people merge are disproportionately sensitive. Contracts, medical letters, bank statements, passport scans, signed agreements. That is worth saying before anything else, because it is the reason the question matters more here than on a tool that resizes holiday photographs.

What we can tell you exactly. The files are uploaded, merged with qpdf, and returned. The upload is deleted the moment the merge finishes; the result is deleted on a thirty-minute timer swept every five minutes, so nothing survives past about thirty-five. There is no account, no history, and nothing is read by a person or used to train anything.

What we cannot give you is proof. You are relying on a stated retention policy, exactly as the earlier version of this section warned — you cannot verify a deletion you did not watch, and you cannot audit who had access. That is true of every online tool including this one, and a page that pretends otherwise is the thing to distrust.

So if the document is sensitive enough that this matters, do it locally. qpdf is free and merges PDFs in one command on your own machine:

qpdf --empty --pages a.pdf b.pdf -- merged.pdf

That is the same program this page runs, doing the same job, without the upload. This tool exists for the case where installing something is not worth it — which is most cases, and not all of them.