What a merge keeps, and what it leaves behind
Merging is the one job on this site where the result can look perfect and still be wrong for what you need it for. Every page arrives exactly as it was, with its text still selectable and its artwork still sharp. What does not arrive is everything that sat around the pages: the form fields people were going to type into, the bookmarks they were going to navigate by, and the tags a screen reader was going to read. This page says what to check before you send it.
Which tool you need
Two or more whole PDFs, one after another
Merge PDF is the tool for it. Up to twenty files in one job, and the arrows on each file set the order they are written in.
Only some pages from each file
Still Merge. Every page of every file appears in one preview in the order it will be written, and any page can be left out of the merged file, moved, or rotated before you download.
One document whose pages need rearranging, with nothing to add
Organize PDF. Merging one file with nothing does nothing; Organize is the page built for reordering, and it can pull pages in from another PDF when you do need them.
Photos or scans that are not PDFs yet
JPG to PDF or PNG to PDF first. Merge takes PDFs, so pictures become a document there and can then be merged with the rest.
One of the files asks for a password
Merge names the locked file and refuses it, so you know which one to deal with. Unlock PDF on that file first, if you know its password, then merge the unlocked copy.
The merged file needs to be smaller
Merge first, then Compress PDF on the result. Merging changes nothing about how the pages are stored, so the merged file is about as large as its parts added together.
What the merged file loses
Your pages are copied, not re-saved: nothing drops to a lower resolution and nothing is turned into a picture. Ordinary links still work, and the merged PDF keeps the title, author and other document details of the file its first page came from.
What does not come across is what sat around the pages. Fillable forms stop working, and bookmarks, tags, layers, attachments and page labels are not carried into the merged file. An existing digital signature may stop being valid, because the merged copy is a new document — your originals are untouched either way.
So if the point of the merged file is that someone fills it in, or navigates it by bookmarks, or reads it with a screen reader that relies on tags, merging is the step that takes that away. Send the parts, or rebuild what you need in the merged copy.
How many files, and how large
Twenty files in one job. That is a fixed ceiling rather than a per-device one, so it is the same number on a phone as on a laptop.
What the job can actually finish is a separate question, and it is decided by the browser on the device you are using rather than by a plan. A merge too large to run safely is refused as soon as you add the files, before any merging starts, so you find out at the beginning rather than halfway through.
What to know before you start
- A password-protected PDF cannot be merged. Merge names the locked file rather than failing vaguely. Organize PDF can show you inside one once you enter its password, but it cannot save a new copy of one either, so unlocking first is the only route.
- Your original files are never changed. The merged PDF is a new file saved to this device, and everything you opened is left as it was.
- Nothing is uploaded. The merge happens in your browser, and the merged PDF is saved to this device; nothing is sent anywhere unless you choose Share.