The tool parses each selected PDF, visits sources in the visible row order, and copies every page index from first to last into a fresh document. The page stream order is deterministic: it never alternates files or sorts by file name. This makes complete-file assembly predictable while deliberately excluding page-level editing.
Visible rows define page sequence
If source A has two pages and source B has three, order A then B yields A1, A2, B1, B2, B3. Moving B above A yields B1, B2, B3, A1, A2. Selection is additive, so newly chosen valid files appear after current sources until you move them.
Understand the fresh document boundary
PDFMerge writes a fresh PDF containing copied visible pages. It does not promise preservation of document metadata, bookmarks, page labels, embedded files, portfolios, XFA, JavaScript, open actions, optional layers, tagged structure, PDF/A or PDF/X conformance, usage rights, encryption, incremental revisions, or digital signatures. A signature in a source does not sign the output.
Inspect the downloaded PDF
Open the exact downloaded file in the reader used by its destination. Confirm the complete page sequence, page count, visible content, links, annotations, form behavior, accessibility, and any destination-specific requirements. Keep the sources: a successful page copy is not a certification that every PDF feature was preserved.