Does Turnitin detect AI in a PDF?
Partly
Yes if the PDF contains real text. No if it is a scan or an image of text, because there is nothing to read.
How it works
Turnitin extracts the text layer. A PDF exported from a word processor has one. A photographed or scanned page is a picture, and the AI detector has nothing to score.
The part people miss
Submitting an image-only PDF to avoid a score is transparently detectable as a behaviour, even though the AI score itself comes back empty.
Flagged for something you wrote yourself?
There is a right order to handle it in, and editing the document first destroys your best evidence.