Outlines (the panel a PDF reader shows as "Bookmarks") are a separate top-level structure inside a PDF. They are not derived from anything visual — they are an explicit, hand-built (or tool-built) …
"This PDF has a password" can mean two very different things, and they behave differently in a combine. The PDF specification calls them the user password and the owner password; together with a pe…
CombinePDF accepts both PDFs and images: photos from a phone, screenshots, scans, even SVG diagrams. Each one becomes a page in the output. The surprise that catches people: those pages don't all l…
A PDF carries two parallel metadata systems: the Info dictionary (a simple key-value map, present since PDF 1.0) and the XMP packet (an embedded RDF/XML document, added in PDF 1.4 and required by P…
You cannot combine two PDFs by appending the bytes of one file to the end of another. PDFs are not text streams — they are random-access object databases with a cross-reference table at the end poi…
One of the under-discussed facts about PDF combining is that the result does not need a single page size. PDF was designed page-by-page from the start: every Page object carries its own MediaBox, a…
Every PDF declares its version near the top: a header line like %PDF-1.7, plus an optional version override in the catalog. Combining two PDFs of different versions raises a small but real question…
"Order" sounds like one thing, but PDFs carry several orderings at once. When you combine two files, only one of them — the visual page order — is reliably preserved. The others either get patched …