Combine several PDF documents into a single file, in the order you choose. Useful when a contract and its annexes, or a month of scanned invoices, should travel as one document instead of fifteen attachments.
Merging is for documents that logically belong together: a signed cover page followed by the schedule, a report with its appendices, chapters exported one by one from a word processor, or a batch of scanned pages that arrived as separate files. The result keeps the pages you selected and nothing else, so it is also the cleanest way to assemble a submission without re-typing anything.
If instead you need to remove material, merge is the wrong tool: split the file first, or use Remove Pages, and then merge what survives.
The order of the files is the order you add them. If the result comes out shuffled, the usual cause is that the files were selected from a folder listing sorted by name rather than by the sequence you had in mind — reorder them before running the tool, not after.
Password-protected PDFs cannot be read until they are unlocked: remove the password first with the Unlock tool, then merge. Very large jobs can also exceed the per-request size limit, in which case merge in two passes rather than one.
There is no fixed count; the practical limit is the total upload size for a single request. Dozens of ordinary documents are fine.
Page content is preserved exactly. Internal bookmarks that pointed inside the original documents can end up pointing at the wrong page once the pages move into a new file, so check the outline if the document relies on it.
Yes, but two documents that both contain form fields can collide in the result. Flatten or remove the fields first if the form must stay fillable.