Why Two Identical PDFs Have Different SHA-256 Hashes
· 9 min read
I spent a long time figuring out why sha256sum invoice.pdf returns a different hash every time my accounting software re-exports "the same" document.
Turns out this is a fundamental property of the PDF format - and it quietly breaks a number of real-world systems that depend on stable file hashes: deduplication, audit trails, content-addressed storage, integrity verification.