Overview
Merging PDFs is the opposite of splitting: several files become one packet you can email, archive, or upload to a portal that only accepts a single attachment.
Order is the whole job. Put cover letter, then resume, then certificates, not the reverse, before you download. The merge runs in the browser, so HR packs and tax bundles never hit a third party converter.
This concatenates pages. It does not restyle fonts or rebuild bookmarks from scratch. If one file is a scan and another is a digital export, the combined PDF will still look like both originals stacked.