A signed invoice from a vendor looks slightly off — the line items don't match the email you got last week. Has it been edited? Here's how to tell, before you pay.
Check the metadata
Open the PDF's document properties. Look for:
- Creation date vs modification date — if they differ, the document has been edited since creation. - PDF producer — the software that last touched the file. If the original was Adobe Acrobat and the producer is now PDFsam, the file's been through another tool. - Title and author fields that don't match the document content.
Metadata is the first place edits show up.
Inspect the signature panel
If the PDF was digitally signed, any post-signing edit invalidates the signature. Open in Acrobat or a modern PDF viewer; if the signature panel says 'Invalid' or 'Signature has been modified', the document has been altered.
For electronic signatures (no embedded certificate), check the audit trail's document hash against the current file. Mismatch = altered.
Look for visual inconsistencies
Edited text often shows:
- Different font weight or kerning from surrounding text. - Anti-aliasing artefacts where text was inserted. - White boxes covering original text (the classic 'cover and re-type'). - Misaligned line spacing after a paragraph.
Zoom to 400% and scan suspect areas. The human eye is good at this.
Cross-reference with the sender
If something feels off, ask the sender for the original file directly — fresh from their system. Compare hashes. If they don't match what you received, the file was altered in transit or by an intermediary.
For critical documents (contracts, invoices), this should be routine, not exceptional.
FAQ
Does saving a PDF count as editing?
Re-saving without changes usually doesn't alter the content stream, but it can update the modification date. Save-then-edit always alters.
Can I edit a PDF without leaving traces?
No. Even careful edits leave metadata and structural fingerprints. Forensic tools usually catch them.
What if the metadata shows no modification but the document looks edited?
Some tools strip metadata when exporting. Combine metadata checks with visual and forensic inspection.
How can I prove a PDF wasn't edited?
Sign it through a platform that records a cryptographic hash. Anyone can verify the hash later to confirm no changes.
Trust but verify. For documents that matter, sign through Flint and store the audit trail with the file.