How to merge PDF files
Drop your files onto the box or click to browse. Each one shows its page count as it loads, which is the quickest way to spot that you grabbed the wrong version of something.
Set the order with the up and down buttons. Top to bottom in the list is first to last in the finished document. The X button drops a file you did not mean to add.
Press merge and download. Your combined file arrives as merged.pdf with no email step and no link to wait on.
What merging actually does to your file
Nothing gets re-encoded. A PDF is a container. Merging lifts the page objects out of your source files and drops them into one new container, and it never touches the images or text inside them.
So merging costs you no quality at all. A 300 dpi scan stays 300 dpi. Text stays selectable. Embedded fonts render exactly as before. Compare that to the print-to-PDF trick people fall back on, which rasterises every page and quietly wrecks all of it.
Size-wise, expect roughly the sum of the parts. A 1 MB file plus a 2 MB file lands near 3 MB. It often runs a little over, because each source can carry its own copy of the same font. A smarter tool would deduplicate those. Need it smaller? Compress the merged file afterwards. Do not try to shrink the pieces first.
Merging breaks digital signatures
This one catches people out on contracts, and it is worth understanding before you merge anything signed.
A digital signature covers the exact bytes of the document at the second it was applied. Page order, internal references, file structure, all of it. Merging rewrites that structure by definition. The cryptographic hash stops matching, and the signature either reports as invalid or disappears from the file. Nothing broke. Catching that change is the entire job of a digital signature.
Two ways around it. Keep the signed file separate and send it alongside the merged pack, which is what most legal and finance workflows expect anyway. Or merge everything first and sign once at the end, so the signature covers the finished document.
A drawn or typed signature image is a different animal. It is artwork sitting on the page. No cryptographic claim, nothing to invalidate, and merging leaves it exactly as it was.
What else can change
Form fields are the common surprise. Two source PDFs that both contain a field called name end up in one document with a naming collision, and depending on the reader, filling one can populate both. Flatten your forms before merging if the values already matter.
Bookmarks and outlines frequently do not survive, since they point at page positions inside the original document. Internal links between pages of one source can break for the same reason. Links out to the web are usually fine.
If your sources were PDF/A for archiving, the merged file will not stay compliant unless every input was PDF/A of the same flavour. Anyone merging for a records system should validate afterwards rather than assume.
Mixed page sizes print badly
A4 is 210 by 297 mm. US Letter is 216 by 279 mm. Letter is 6 mm wider and 18 mm shorter, which sounds like nothing until you print.
Merge one of each and you get a single PDF holding both sizes. On screen you may never spot it. Send it to a printer and you get uneven margins, or a driver that scales half the pages and leaves the rest alone.
This tool resizes nothing, and that is the right default. Silently stretching someone's signed contract onto different paper would be the worse bug. Want one consistent size? Standardise the sources, then merge.
Scanned pages cause most of these. Phone scans and flatbed scans rarely agree on exact dimensions even when both say A4.
When people merge PDFs
One attachment instead of five is the everyday reason. A finished report, a signed agreement plus its appendices, an application packet with a CV and a cover letter and three certificates.
Upload portals force it too. Plenty of government forms, university submissions, and job applications accept exactly one file, so merging is not a convenience there, it is the only way through.
Then there is the archive case. Freelancers stitch an invoice, a contract, and proof of work into one client record. Home buyers combine bank statements and ID scans for a mortgage file. Students merge a term of lecture handouts into one searchable document.
Frequently asked questions
Is there a limit on file size or number of pages?
No fixed limit. The practical ceiling is the memory on the device you are using, so a phone will give up before a laptop does.
Can I merge a password-protected PDF?
Often, but not always. A file with a strong open password will fail. Remove the password first, then merge.
Will merging reduce the quality of my scans?
No. Pages are copied, not re-encoded, so a 300 dpi scan stays a 300 dpi scan.
Why is my merged file so large?
Because it is the sum of its parts, plus any duplicated fonts. Compress the merged file afterwards if you need it smaller.
My signature disappeared after merging. Is that a bug?
No. A digital signature is invalidated by any change to the document structure, and merging is a change. Merge first, then sign the finished document.
Do bookmarks carry over?
Usually not. Bookmarks reference positions in the original file, and those references do not survive being copied into a new document.
Related: turn images into a PDF before merging · compress the merged file · reorder pages afterwards · sign the finished document.