Fingerprint a PDF So Every Copy Points Back to Its Owner
or drop files here
List who is getting the document and receive a separate copy for each, quietly signed with its own code. Your recipient list is turned into files on this computer and never travels to a server.
One file per person, one code per file.
Start from the clean original
Use the unmarked master file. If you drop in a copy that already carries a mark, the tool warns you before a second one is layered on.
Name each recipient
One person or team per line. Each line becomes its own PDF with a fresh random code, and you choose whether a "Copy for" footer is printed too.
Send, then trace if needed
Save the ZIP and send each person their own file. If one surfaces somewhere unexpected, switch to Check a copy and drop it in.
When you need to know whose copy it was.
Sending one identical file to twenty people means a leak could have come from any of them. Twenty slightly different files turn a guessing game into a lookup.
Board and investor packs
Quarterly numbers sent to directors or a shortlist of investors are tempting to forward. A personal copy for each makes it clear who passed the deck along.
Advance review copies
Authors and publishers sending a manuscript to early readers or critics can mark each PDF, so a pirated copy on a sharing site points back to its source.
Exam papers sent to centres
Give every school or test centre its own copy of a paper ahead of the sitting. If questions appear online early, the code narrows the search to one site.
Scripts and embargoed releases
A screenplay draft for the cast or a press release under embargo can carry a visible "Copy for" line that discourages sharing before the date.
Sensitive internal memos
Restructuring plans or salary bands shared with a handful of managers. Personal copies give you a starting point if one turns up in a group chat.
Proposals to competing bidders
When the same brief or pricing schedule goes to several suppliers, separate marked copies show which one let it reach a rival.
Where the mark hides, and what wipes it out.
Each copy gets a code of eight characters drawn at random from Crockford's base32 alphabet, which leaves out I, L, O and U so a code read aloud over the phone cannot be confused. That is about 1.1 trillion possible codes, so two recipients will not end up sharing one by accident.
The code and the name are joined into one short string and stored in three separate places, because each one is fragile in a different way. Spreading the mark out means a copy that has been re-saved, scrubbed or reprinted still has a good chance of keeping at least one of them.
Be realistic about the ceiling, though. All three carriers live in the file's data, not in the picture of the page, so nothing hidden survives a camera, a scanner or someone typing the content out again. Against that kind of leak, only the visible footer helps, and only as a reminder that discourages it in the first place.
Invisible text line, every page
Set in 1 pt type using the PDF's invisible rendering mode near the bottom-left corner. It is part of the text layer, so it rides along through most re-saves and printers that keep text.
Document properties entry
A custom key added to the document information dictionary. Easy to read back, but also the first thing a metadata cleaner removes.
Trailer file ID
The second half of the ID pair every PDF carries is replaced with the code. There is no room for the name here, which is what the key CSV is for.
Visible footer (optional)
A small grey "Copy for {name}" line centred at the foot of each page. Characters outside the Western European set print as "?", though the hidden mark keeps the exact name.
| What the recipient does | Hidden text line | Properties entry | File ID | Visible footer |
|---|---|---|---|---|
| Forwarded by email, chat or a shared drive | Kept | Kept | Kept | Kept |
| Opened and re-saved in a PDF editor | Kept | Usually kept | Often replaced | Kept |
| Printed to a new PDF ("Print to PDF") | Usually kept | Lost | Lost | Kept |
| Run through a metadata scrubber | Kept | Lost | Depends on the tool | Kept |
| Pages converted to images | Lost | Lost | Lost | Kept as pixels |
| Screenshot or phone photo of the screen | Lost | Lost | Lost | Only if in frame |
| Printed on paper, then scanned | Lost | Lost | Lost | Unless cut off |
| Text retyped or pasted into a new file | Lost | Lost | Lost | Lost |
"Usually" and "often" are deliberate: PDF editors and virtual printers differ, and some rebuild text in ways that drop invisible lines. A person who knows the mark exists can also delete it on purpose. If tracing really matters, test your own workflow once by fingerprinting a copy, passing it through the same steps, and running Check a copy on the result.
Questions answered.
What exactly is added to each copy?
Will the person receiving it notice anything?
Does the mark survive printing, photos or screenshots?
Can someone remove the fingerprint?
Can other people read the recipient's name from the mark?
What is fingerprint-key.csv for?
Why does Check a copy say no mark was found?
What is the SHA-256 shown in Check a copy?
Are the recipient names or the document uploaded?
More tools you might need.
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