When merging PDFs saves you time
Job applications, visa files and loan paperwork often ask for one PDF, while your documents sit in five separate scans. Merging puts them in a single file so nothing gets lost in an email thread. Accountants use it to bundle monthly invoices, and students use it to combine chapter notes before printing.
The page order in the merged file follows the order of the list. Check it before you press merge, since fixing the order afterward means another pass.
A typical example is a rental application. You have a photo ID scan, three payslips, a bank statement and a reference letter, each a separate file. Merged in that order, the landlord opens one document and finds everything where they expect it, which makes approval quicker.
It also helps when you print. One merged file means one print job, with no chance of a page from a different file being left in the tray.
Getting the order right
Drag each file by its handle to move it. A good habit is to name files with a leading number, such as 01-cover.pdf and 02-resume.pdf, so they start in the right sequence when you select them together. Some systems add files in the order you clicked them, others alphabetically, so double check the list.
If you only need part of a document, trim it first with the extract pages tool, then merge. That avoids carrying along blank pages or cover sheets you do not need.
After merging, scroll through the result once. Look at the point where one file ends and the next begins, because that is where a duplicated or missing page would show up.
What stays and what changes
Pages are copied across as they are, so text stays selectable, links keep working and images are not recompressed. Page sizes can differ between files. A mix of A4 and Letter pages is allowed, and each page keeps its own size.
Bookmarks and form fields from the source files may not all carry over, so if a fillable form matters, fill it in before merging. Password-protected or encrypted PDFs cannot be opened by this tool. Remove the protection in the program that created them first.
Fonts are embedded in each source file, so the merged document looks the same as the originals on any device. File properties such as title and author come from the new document rather than the sources.
File size after merging
The merged file is roughly the sum of its parts. If it is too large to email, run it through the compress PDF tool afterward. Normal mode makes small savings and keeps text selectable. Strong mode makes bigger savings but turns pages into images.
Because the work happens in your browser, a very large merge uses your device's memory. On an older phone, split big jobs into two smaller merges.