A PDF is more than a stack of page drawings. It can carry catalog-level navigation, embedded files, scripts, form systems, signatures, conformance declarations, permissions, and incremental history. Page copying targets visible page content and referenced page resources; it is not a byte-for-byte concatenation of source containers.
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.
Treat signatures as invalidated context
Digital signatures bind a particular source revision. A newly serialized document has different bytes and is not signed by those source signatures. Do not use PDFMerge to claim that a resulting file is signed, certified, archival, compliant, or evidentiary.
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.