Merge PDF

Order is the one thing every merge has to get right, and it is easy to get wrong when a dozen files are involved. By default the files are combined in Upload order, the order in which they appear in the list. You can drag any file up or down before pressing the merge button, so the list on screen is exactly the order of the finished document.

For larger sets, sorting is faster than dragging. File name sorts the names naturally, so a file called page 2 comes before page 10, which a plain alphabetical sort gets wrong. This works well when your files are numbered, such as scans saved as scan 1, scan 2 and so on. Date modified puts the oldest file first, which suits a series of statements or reports saved month by month.

If the order you need does not match the names or dates, rename the files before uploading, or simply drag them. A short check of the list before merging saves a second round, because once pages are in one file, rearranging them means splitting and merging again.

Each source file starts right after the last page of the one before it. When the merged file will be printed on both sides of the paper, that can leave a document starting on the back of the previous one. Turn on Start each file on an odd page and a blank page is inserted where needed, so every document begins on the front of a new sheet.

Phones and scanners often save documents with names made of dates and numbers that say nothing about the content. Renaming them before you upload is worth the minute it takes: the names decide the sort order when you merge by name, and they become the bookmark titles readers see in the finished file.

Files from different places rarely share one page size. A letter typed in the United States uses Letter paper, a scan from Europe is usually A4, and a phone scan may have any shape at all. By default, Page size is left at Same as source and every page keeps its own size. That is the safest choice, because nothing on the page changes.

When the merged file needs a uniform look, for printing or for a portal that checks page size, pick A4, Letter, Legal, A3 or A5. Then decide what happens to the content. Scale to fit enlarges or reduces each page so all of it fits the new size, which may leave white margins when the proportions differ. Keep size, center leaves the content at its original scale and centers it on the new page, which avoids any scaling but can crop pages that are larger than the target. To change page sizes without merging, use Resize PDF.

Bookmark per file adds an entry named after each source file to the bookmark panel of the merged PDF. Readers can then jump straight to a particular document instead of scrolling, which makes a merged report, a set of invoices or an application pack much easier to move around in. Since the entry uses the file name, it pays to give the files clear names before uploading, such as Passport, Bank statement or Reference letter, rather than the numbers a scanner assigns.

Remove blank pages drops pages with no visible content. It is meant for scanned stacks where the backs of single-sided sheets were captured as empty pages. Leave it off when blank pages are deliberate, for example separator pages in a printed booklet.

Two clean-up options round things off. Flatten forms turns form fields into plain page content before merging, and Remove metadata deletes author, title and software information carried over from the source files.

If the result is not what you expected, the cause is usually one of a few things. Documents in the wrong order mean the list was not checked: sort by File name for numbered files, or drag them into place, and merge again. Form values that changed or repeat across documents come from fields with the same name, which now share one value; merge again with Flatten forms on. Pages of very different sizes call for one size under Page size with Scale to fit.

A file that is rejected may need a password to open or may be damaged; unlock it with its password, or open and save it again in a PDF viewer. And a merged PDF that is too large to email can be compressed, or split into parts that each fit the attachment limit.

Merging copies the pages and their content as they are, so the result keeps text that can be searched and copied, links inside each document, and the quality of every image. It does not compress anything, which is why the merged file is roughly as large as all the source files added together.

Merging also does not change what is inside each page. Comments, highlights and stamps that were added in a PDF reader come along with their pages, and so do links to websites. If the merged file is meant as a clean final copy, flatten it or remove comments before sharing it outside your team.

Digital signatures are the one thing that cannot survive a merge intact. A signature covers the exact file that was signed, and the merged document is a new file, so readers will no longer show the original signatures as valid. When a signed contract has to be sent with other papers, keep the signed PDF as a separate attachment, or merge only for reading and keep the signed original as the record.

Merging is the counterpart of splitting. Together, the two let you rebuild a document: take pages out of several files with Split PDF, then merge them into the order you want. More options for working with PDF files are listed under PDF tools.