You have two scans of a contract and need one file. Or a passport copy plus a utility bill for a bank. The obvious answer is Adobe Acrobat, and the obvious problem is that merging PDFs is behind a subscription.
The good news: you do not need Acrobat for this. The less obvious news: most of the free alternatives ask you to upload your documents to their servers first, and the documents people merge are rarely the ones they would happily hand to a stranger.
Way one: the tool already on your Mac
Preview merges PDFs and it is already installed.
Open the first file, show the thumbnail sidebar, then drag the second PDF into it. Export the result as a new file.
Works well when. You are on a Mac, the files are yours, and this is a one-off.
Where it stops. Mac only. The sidebar drag is famously fiddly: drop the file on a page instead of between pages and you get an attachment rather than merged pages. And Preview has quietly corrupted output on large scans often enough that people keep the originals until they have checked the result.
Way two: Windows, without extra software
Windows has no built-in PDF merger. What it does have is "Microsoft Print to PDF".
Select the files, print each into a single PDF, or open them in a browser and print into one file. In practice this means printing one file, then the other, then merging those two, which brings you back where you started.
Works well when. You need to merge a handful of pages and the quality of the result does not matter much.
Where it stops. Printing to PDF re-renders the pages. Text stops being text and becomes a picture of text: the result is no longer searchable, cannot be copied from, and gets heavier. For an invoice that is fine. For a contract you will need to quote from later, it is not.
Way three: online services
iLovePDF, Smallpdf, PDF Candy and the rest. Drag two files in, get one back.
Works well when. The document is not sensitive, and the free daily limit covers you.
Where it stops, and this is the part worth reading. Every one of these sends your file to their server. It is processed there and stored for a while: the usual promise is deletion after an hour or a few hours. You are trusting a company you have never heard of with a document you would not email to a stranger.
Practically: passport scans, contracts with figures in them, medical records and anything with your bank details in it go up to somebody else's machine. Most of the time nothing happens. The question is whether you want it to be a question at all.
The free tiers also cap you — typically two or three operations a day, and a file size limit that a scanned contract can exceed on its own.
Way four: merge in the browser, with no upload
There is a fourth option that is easy to miss, because from the outside it looks exactly like way three: you open a web page and drop files onto it.
The difference is what happens next. A browser PDF editor reads the file with your own browser and rebuilds it there. The pages never travel anywhere.
We checked this rather than taking the description on trust. With every network request recorded while two PDFs were merged, the count of requests carrying PDF content was zero — the merged document existed only in the browser tab.
That is not a promise about our intentions. There is simply nothing to store: the file is never sent, so no retention policy applies to it.
Works well when. The document is sensitive. You are on a computer where you cannot install anything. The file is large. You need this more than three times a day.
Where it stops. The tab has to stay open while you work, because the work happens in it. Very large files are limited by the memory your browser tab is allowed, not by any rule we set. And a digital signature does not survive a merge — that is not a limitation of one tool, it is what merging does to a signed PDF. We tested this: the signature form is dropped when pages are copied into a new document. If your PDF is signed and the signature matters, do not merge it. Send the files separately.
Which to pick
| Situation | What to use |
|---|---|
| Passport scan, contract, anything private | Browser tool, no upload |
| One-off merge on a Mac, file not sensitive | Preview |
| The result must stay searchable text | Anything except print-to-PDF |
| More than a few merges a day | Browser tool, no daily cap |
| The PDF is digitally signed | Do not merge at all |
The short version: merging PDFs is a solved problem and has been for years. The only real question left is who gets to see the document while it is being solved.