Merge PDF Files

Combine several PDFs into a single file without installing software or uploading anything. Add your files, arrange the order, and download the merged PDF — all in your browser.

How to use

  1. Select or drag in the PDF files you want to combine.
  2. Arrange them in the order you want.
  3. Merge and download the combined PDF.

Merging copies the original pages across without re-encoding them, so text stays sharp and scans do not get muddier. Layout and annotations survive; some interactive pieces — form fields, signatures — may not.

In depth

Merging does not re-encode anything

This tool copies page objects from the source files into a new document. Images are not recompressed and text is not redrawn.

Scanned pages therefore stay exactly as sharp as they were, and text remains selectable, searchable and copyable. The output size is roughly the sum of the inputs.

"Merging degraded my quality" is a symptom of tools that rebuild the pages. It does not happen here.

What survives and what does not

Survives — page content, embedded fonts, images, page size and orientation, and the text layer.

May be lost — form fields, digital signatures, document-level JavaScript, some annotations, bookmarks and file attachments.

Digital signatures always break. A signature attests that a specific sequence of bytes is unchanged, and merging rebuilds those bytes. Send signed contracts as their original files rather than merging them.

Fillable forms tend to flatten or lose their fields too. Print to PDF after filling them in, then merge the flattened result.

Getting the order right

File order becomes page order, and you can drag to rearrange after adding.

If you plan to rely on filename sorting, pad your numbers: 1, 2, 10 sorts as 1, 10, 2, while 01, 02, 10 sorts as intended.

Scans of double-sided documents often arrive as separate odd and even batches. That needs interleaving rather than simple concatenation — rescanning in duplex mode is usually faster than fixing it afterwards.

Password-protected files

PDFs carry two kinds of password: an open password required to view the document, and a permissions password restricting printing, editing or copying.

Files with an open password cannot be read by the browser and cannot be merged. Remove the password and save a copy first.

Files with only a permissions password will open, but working around that restriction disregards the owner's intent. Don't, unless the document is yours.

When pages are different sizes

Mixing A4 and Letter keeps each page at its original size. Nothing is scaled to match, because scaling would mean re-rendering the content.

On screen this is invisible. In print the margins jump around, so unify the page size before merging anything you intend to submit.

The same applies to mixed portrait and landscape pages: readers end up rotating the view page by page. Rotating them to a consistent orientation first — /pdf-split does this — avoids that.

Files never leave your device

Merging happens inside the browser, so contracts, medical records and financial documents do not cross the network.

This matters in practice because PDF merging is a common enough task that most online services upload your file. Even with a deletion promise, the document exists on someone else's disk for a while — and plenty of corporate policies prohibit exactly that.

The limit is browser memory: several very large files at once can slow or stall the tab. Split the work when that happens.

FAQ

Is my PDF uploaded anywhere?

No. Files are merged locally in your browser, so your documents never leave your device.

Can I change the order of the PDFs?

Yes. Arrange the files in the order you want before merging, and the pages are combined in that sequence.

Is there a limit on file count or size?

There's no fixed limit, but everything is processed in your browser's memory, so a large number of very big files can slow things down.

Method and sources

What this tool bases its numbers on, and how far those numbers go.

What this tool is
It copies pages between documents. Page content survives intact; the interactive layer around it — signatures, form state, some annotations — is what breaks.
Formula
Pages are copied as objects from each source document into a new one in the order you set, with their content streams and embedded fonts carried across rather than re-encoded. Text stays vector text and scans keep their original compression, so nothing loses quality. Everything runs in the page — no file is uploaded.
Worked example
Merging a 10-page file with a 5-page file gives 15 pages, and the output size is close to the sum of the two inputs because nothing is recompressed.
Limitations
  • Digital signatures do not survive. A signature covers the exact bytes of the document it signed; producing a new document necessarily invalidates it. Merge signed PDFs only when the signature no longer needs to verify.
  • Form fields can collide. Two source files with fields of the same name merge into one field with shared state, and some form structures are dropped rather than merged.
  • Bookmarks, outlines, tagged-PDF structure and document-level JavaScript may not carry across. What you get is reliably the pages, not reliably the document furniture.
  • Encrypted or password-protected PDFs cannot be read. There is no way around that from inside the page, and it is not a bug.
  • Memory bounds the job. Merging many large scanned files at once can fail part-way on a phone, since the whole result is assembled in the browser.
Effective date
Last reviewed

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