Flatbed scanners and phone scanner apps love producing one file per page. Anyone receiving fourteen separate attachments will not thank you.
Check the order carefully: filenames ending in 10 can sort ahead of those ending in 2. A multi-page source moves as a group; extract individual pages first if the group is not appropriate.
Pages are copied without rasterising their content. Merging does not compress the resulting document.
Check document-level forms, bookmarks, links and signatures separately: rewriting a PDF does not guarantee they survive unchanged.
After you merge, scroll through the result once. Each file keeps its own page size, so scans from different machines can come out at slightly different sizes. That is normal, and it is only worth fixing if the recipient will notice.
The list shows how many pages each file has, and the merged result shows the total. If the total is not what you expected, a file is missing or in the wrong place. A page that came out sideways can be fixed afterwards with Rotate & reorder. Numbering your scan files 01, 02, 03 before you add them keeps them in order when you select them together.
No. It combines pages. Raster compression is a separate operation and removes searchable text.
A PDF that needs a password to open must be unlocked first with Protect PDF. For a very long document the thumbnails can take a moment, and you can still type the page numbers yourself.
Yes. Any PDFs can be joined, and each page keeps the look it had.