How to Merge PDF Files

Select two or more PDF files.
Drag the files into the order you want them combined.
Review the combined page sequence in the thumbnail rail.
Merge and download the final PDF.

What this tool changes

Combines pages from every selected file into one new PDF, in the order you set.

What it preserves

Original page size and orientation of each source page.

Good to know

Interactive form fields, embedded digital signatures, and some annotations may be flattened or altered when pages are combined.
Encrypted source files must be unlocked before they can be merged.

Files combine in the order you add them

Not alphabetically, and not by date. When you select twenty files at once, your operating system decides the order it hands them over, and that order is rarely the one you want. The thumbnail rail shows you what you actually have before anything is combined, which is the moment to fix it.

For a batch that has to land in a specific sequence, either add the files deliberately one group at a time, or add everything and drag. On a long batch it is far quicker to rename your sources with a numeric prefix — 01-, 02-, 03- — before you start than to reorder fifty thumbnails afterwards.

The step people skip and then regret is looking at the rail at all. Combining is the easy half; getting the order right is the half that goes wrong, and a misplaced document is much easier to spot as a picture than as a filename in a list.

Mixed page sizes, and when they matter

Merging an A4 document with a US Letter one produces a PDF whose pages genuinely are different sizes. Nothing is broken — the format allows it, and on screen you will barely notice, because viewers scale each page to fit the window.

On paper you will notice. A printer resolves the difference by scaling or by shifting, and either way one set of pages comes out with different margins from the other. A4 is 595 × 842 points; Letter is 612 × 792 — wider and shorter, which is why a mixed document looks subtly wrong in a way that is hard to name until you measure it.

Cropping trims page boundaries; it does not scale all content to a common paper size. If a submission requires uniform pages, use suitable source or print-scaling settings and inspect the result before merging.

Large batches and your browser

Everything here runs on your own machine, which means your memory is the ceiling rather than a server's. Combining dozens of large scans can reach it, and a tab that gives up mid-merge is a resource limit rather than a bug.

Smaller batches may reduce peak memory use, but the final merge still needs memory for its inputs and output. Repeated rebuilds are not guaranteed to produce an identical file or preserve document-level features.

If the source files are very large to begin with, that is worth addressing first — a scan at an unnecessarily high resolution is heavy for reasons that have nothing to do with merging. Why is my PDF so large covers what actually makes a document heavy.

What the merged file inherits, and what it does not

A merge builds a new document and copies pages into it, which raises a question with a surprising answer: whose details does the result carry? We gave two source files different titles and different authors, merged them, and read the fields back. The merged document had neither. Title and author both came back empty.

It does not inherit from the first file, or the largest, or the one you added first. A rebuild starts with a blank document and copies pages, and the pages are all it copies. Bookmarks go the same way, and so does any internal link pointing into a document that is now only part of a larger one.

Read that in the direction that applies to you. If you are combining documents to send onward, the clearing is quietly useful, because the author field is filled in automatically by most software from your computer account and frequently holds a real name — several of them, in a merge. It is not a redaction guarantee, though: it does not reach data held inside embedded images, which what hidden data a PDF carries covers.

If the combined file is meant to be the official version of something, expect to set its title and author yourself afterwards, because nothing in the merge can choose them for you.

Frequently asked questions

Are my files uploaded to a server?: No. Merging happens entirely in your browser using JavaScript. Your PDF content never leaves your device.
Can I reorder pages from different files after merging?: Yes. Every page from every file appears in one thumbnail rail before export, and you can drag or use keyboard controls to reorder them.
What happens to password-protected PDFs?: You will need to unlock a password-protected PDF with its correct password first. PDF Editing Tools does not bypass PDF passwords.
Will digital signatures survive the merge?: This merger creates a new PDF and does not preserve valid certificate signatures over that output. Keep signed originals separately; the merge interface does not provide a reliable signature-detection warning.
Does the merged file keep the title and author of the first document?: No. We measured it: merging two files with different titles and authors produced a document with both fields empty. A merge inherits pages, not document properties — set them again if the combined file needs them.