Merge PDF Files Online

How to Merge PDF Files

1. Select two or more PDF files.
2. Drag the files into the order you want them combined.
3. Review the combined page sequence in the thumbnail rail.
4. 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.

If the combined file is destined for print or formal submission, standardise before you combine rather than after: Crop PDF in its resize mode brings pages to a common size. If it is only ever going to be read on a screen, leave it alone.

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.

The reliable technique is to work in stages: combine five files, then another five, then combine those two results. Each step holds far less in memory than one fifty-file operation, and the output is identical. Closing other tabs genuinely helps, because a browser divides memory between them.

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.