How law firms can check court filings and contracts for hidden AI instructions
Check every document from outside the firm before an AI tool reads it: copy the text out and compare it with the page, and in Word files make all text black and show hidden text.
Courts have already caught filings carrying white or tiny instructions aimed at AI. For any volume, put an automatic check in front of the AI tool, so nothing reaches it unchecked.
The free way to check
For a filing or a contract that arrives as a PDF or a Word file:
- Select all, copy, and paste into a plain text editor. Compare the paste with the page, looking for any sentence you cannot find on the page.
- In a Word file, select all, set the font colour to Automatic and the size to 12, and turn on hidden text (File › Options › Display › Hidden text).
- In a counterparty’s draft, set the Review view to “All Markup” and read every comment and tracked change.
- Check the figures that matter — amounts, dates, caps — in the pasted text as well as on the page.
Where the free way falls short
- A PDF can show one figure on the page and carry a different one in its text layer. An AI that reads the text layer can read $500,000 where you read $50,000, and the paste shows you the difference only if you check that figure.
- Text behind a signature block, a logo or a white box stays hidden in the document itself.
- Invisible Unicode characters paste as nothing at all.
- A long agreement makes a line-by-line comparison slow, and one missed sentence is enough to steer an AI review.
How HiddenContent.ai checks it
HiddenContent.ai checks a filing or a contract before your AI tool reads it, and reports each hidden passage with its page, where it sits and the trick behind it, including a figure on the page that disagrees with the figure in the text. It marks hidden text written as an instruction to a model.
Each result comes with a signed certificate recording this document, this verdict and this engine version. It verifies offline, without contacting us, so the firm keeps a record of what it checked and what it found.
No file leaves our machines, and no AI model reads your document. See one real analysis, end to end for exactly what comes back. Sign up with GitHub for 20 free pages, then a cent a page.
Real cases
- STF identifica primeiro caso de prompt injection na Corte; Zanin vota por multa — Migalhas, 25 Sept 2026
- Person Hides Prompt Injection in Legal Filing Telling AI to Side With Them — 404 Media, 13 Aug 2026
- Lawyers Put Prompt Injection in a Document to Try to Influence the Court's AI Tools: Artificial Intelligence Trends — eDiscovery Today, 2 Jun 2026
The techniques, one page each
- Text the colour of its background
pdf.white-text - Type too small to read
pdf.tiny-font - A figure the page contradicts
pdf.vision-value-divergence - Drawn glyph contradicts stored character
pdf.cmap-divergence - Text covered by something opaque
pdf.occluded-text - Text that matches its background
docx.white-text - Word's hidden text attribute
docx.vanish - Text in a Word comment
docx.comment
Questions
Have courts sanctioned hidden AI instructions in filings?
Yes. A US court banned a plaintiff from electronic filing after he hid 3-point white text in a filing; a Brazilian court fined two lawyers R$84,000 over white text in a petition; and a justice of Brazil’s Supreme Court voted for a fine over small white letters in a petition. All three are on our In the Wild page.
Does an AI review tool see comments and tracked changes?
It can. A Word file keeps comments and tracked changes inside it, and a tool that reads the raw file reads them even when your view hides them.
Can we prove we checked a document?
Yes. Each result carries a signed certificate of the document, the verdict and the engine version, and it verifies offline, years later, without our service.