About

PDFs can hide content that isn't visible on the page: text painted white on white, layers turned off by default, font sizes shrunk to nothing, or instructions tucked in off-page coordinates. As more documents get summarized or reviewed by AI tools, this hidden content has become a way to slip instructions past a human reader and straight to the model reading the file on their behalf.

WhatsInMyPDF checks a PDF for these techniques: invisible render modes, white-on-white text, tiny fonts, text positioned off the page, crop box mismatches (the signal left behind when content is cropped off the page), hidden optical content groups, embedded files, JavaScript, annotations whose text hides in the file structure, and known prompt-injection phrasing. Everything runs in your browser using WebAssembly. Your file is never uploaded anywhere.

This is a free, open-source tool. It won't catch everything, and it isn't a substitute for careful review, but it surfaces the signals that are easy to miss by eye.