How to find hidden text in a Word document before you give it to an AI
Select all the text, make it black and a readable size, and turn on Word’s display of hidden text, then read the document again. That reveals the common tricks.
It misses text behind pictures and shapes, text placed off the page, and characters that draw nothing at all.
The free way to check
Work on a copy of the file, so nothing you change goes back to the person who sent it.
- Press Ctrl+A (Cmd+A on a Mac) to select everything. Set the font colour to Automatic, the size to 12, and the highlight to No Color. White text and tiny text now show up.
- Turn on hidden text: File › Options › Display, then tick “Hidden text” (on a Mac, Word › Settings › View). Word now shows text formatted as hidden, with a dotted underline.
- Open the Review tab, set the view to “All Markup”, and read the comments and tracked changes.
- Open the Selection Pane (Home › Select › Selection Pane). It lists every picture, shape and text box, including ones you cannot see. Move or hide each one to check what sits underneath.
Where the free way falls short
- Text behind a picture or a shape stays hidden after you change its colour. You only find it if you move every object.
- Text in a text box placed off the page does not appear on any page.
- Invisible Unicode characters stay invisible whatever colour or size you choose.
- A Word file keeps text in places the page never shows: alternative text on pictures, field codes, unused headers and the document’s properties. Some AI tools read those too.
- Microsoft’s own documentation says Word’s built-in check for hidden content, the Document Inspector, cannot detect white text on a white background (Microsoft Support).
How HiddenContent.ai checks it
HiddenContent.ai reads the Word file’s own structure — its styles, colours, sizes, shapes and where each one sits on the page — and works out what Word would actually show. It compares that with the text an AI reads, including the places a page never shows, and reports each hidden passage with where it sits and the trick behind it.
It reads older .doc files as well as .docx, and it marks hidden text written as an instruction to a model.
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Real cases
- Context Collapse, Part 3 - AI Worming through Word — En Klype Salt, 28 Jul 2026
- From Copilot to Copirate: How data thieves could hijack Microsoft's chatbot — The Register, 28 Aug 2024
- Job applicants are hiding secret AI messages in their résumés — Business Insider, 6 Sept 2026
The techniques, one page each
- Text that matches its background
docx.white-text - Text below readable size
docx.tiny-font - Word's hidden text attribute
docx.vanish - A picture drawn over a text box
docx.occluded-text - Text positioned off the paper
docx.offpage-text - Fully transparent text fill
docx.zero-opacity - Text in a Word comment
docx.comment - A picture description nobody reads
docx.alt-text - Content inside a Word field
docx.field-instruction - Prose in a document property
docx.document-property - Zero-width characters in text
unicode.zero-width - Text coloured to match its background
doc.white-text - Every way text hides in a Word document
Questions
Does Word’s Show/Hide button show all hidden text?
No. It shows text formatted as hidden, along with formatting marks. White text, tiny text and text behind shapes stay hidden.
Can an AI read white text in a Word document?
Yes. White text is ordinary text with a white colour, and most AI tools read the text without the colour. A researcher used exactly this to steer Copilot inside Word: see In the Wild.
Does HiddenContent.ai read old .doc files?
Yes. It reads .doc as well as .docx.