Merge PDF

Merging a PDF is a copy operation, not a re-render. Each page object is lifted out of its source document along with the resources it references — the embedded font subsets, the colour spaces, the image streams — and written into a new document in the order you chose. Nothing is rasterised and nothing is re-encoded, which is why a merged PDF is pixel-for-pixel identical to its inputs. Text stays selectable, vector artwork stays vector, and photographs keep whatever JPEG quality they were saved at.

That matters more than it sounds. The other common way people combine documents — printing each one to PDF, or exporting through a print driver — pushes every page through a rendering stage, and each round trip costs a little sharpness and usually the ability to select text. Copying pages has no generation loss at all: merge the same files ten times and the tenth result is as good as the first.

What does not come across is the handful of structures that belong to a document rather than to any particular page. The bookmark outline is the obvious one, and document-level scripts and the form dictionary are the others. Those exist once per PDF, and three inputs would mean three competing versions with no principled way to pick a winner, so they are left behind rather than merged badly.

Order is most of the job, and it is where merges usually go wrong. Your operating system's file picker does not hand over files alphabetically — it hands them over in selection order, or in whatever order the folder happens to be sorted by. The classic result is a report where Chapter 10 lands between Chapter 1 and Chapter 2, because filenames without zero-padding sort as text rather than as numbers.

So treat the list in the tool as the only thing that counts, not the order you clicked. The arrows move a file up or down, the position is shown as you go, and the merged document follows that list exactly. Checking it takes a few seconds; fixing the order after the fact means splitting the merged file apart and starting again.

Combining a dozen files into one document creates a navigation problem: the reader now has a hundred pages and no idea where the third attachment begins. The optional table of contents solves it by generating a contents page in front of the merged content, with one numbered entry per source file, a dotted leader, and the page number that file starts on.

Those entries are genuine PDF link annotations pointing at a destination in the merged file, not a picture of a contents page. Clicking an entry jumps straight to that document in Acrobat, in Preview, and in the built-in viewers in Chrome, Edge and Firefox. The page numbers already account for the contents pages themselves, so what the listing says is what the reader lands on.

The listing paginates on its own once you merge more files than fit on a page, and filenames too long for the column are trimmed with an ellipsis so the numbers stay aligned. Because the entries are built from your filenames, giving your source files meaningful names before you merge is what makes the contents page useful.

Page geometry is a property of each page, so merging does not normalise it. An A4 contract merged with a Letter invoice produces one document containing both sizes, and pages that were rotated stay rotated. This is the right default — rescaling someone's page would move their margins and reflow nothing, since a PDF page is fixed art rather than a document that reflows. When you do want everything uniform, Resize PDF over the merged output will do it in one pass.

Scanned documents merge exactly like born-digital ones, because a scan is simply a page whose content happens to be one large image. The resolution is preserved and so is the file weight, which is why a merge of scans is usually the case where compression afterwards pays off most.

Only PDFs can be merged directly. To combine photographs or screenshots with your documents, use Merge PDF & Image, which wraps each picture onto a page of its own before combining. Word, Excel and PowerPoint files need converting to PDF first — the matching converters are one click away in the Convert to PDF section.