AI Detector for PDF: Check a PDF for AI Writing (Free)
Most AI detectors want pasted text — annoying when what you actually have is an essay PDF, a report, or a submission export. The fix: use a detector that reads documents directly. Here is the exact workflow for PDFs, including the scanned-PDF and long-document cases.
Check a PDF right now
Open the free AI detector, click Upload, and choose your PDF or DOCX — the text is extracted and scanned in one step, with sentence-level highlighting in the report.
How to check a PDF for AI (3 steps)
- Upload. On the detector page, use the Upload button and pick the PDF (DOCX works too). The tool extracts the document text automatically.
- Scan. Run the detection. You get an overall AI score, confidence level, and — the part that makes it actionable — per-sentence highlighting showing exactly which passages read as AI-written.
- Act on the flags. Reviewing someone else's work? Focus the conversation on the flagged sections. Checking your own? Rewrite those sentences in your voice (the humanizing guide covers how) and re-scan.
Scanned PDFs: run OCR first
If you cannot select text in the PDF, it is a scan — an image of a page. Detectors need text, so run OCR (optical character recognition) first: most PDF readers, Google Drive, and free OCR sites convert scans to selectable text. Then upload the OCR output. Expect minor OCR errors; they rarely change the overall detection result but can affect individual sentences.
Long documents: scan in sections
Word limits apply per scan (1,000 words free, 5,000 on Pro), and section-by-section scanning is genuinely better for long documents anyway: real submissions are often mixed — a human introduction, AI-drafted middle chapters, a human conclusion. Chapter-level scans localize the AI-written sections instead of averaging them away in one document-wide score.
What to check besides the prose
PDFs with references deserve a second pass: AI-drafted documents are notorious for plausible-but-fake citations. Paste the reference list into the free fake citation checker — invented sources are more conclusive evidence than any AI percentage. For choosing the detector itself, our benchmark of 8 free AI content detectors compares accuracy and false-positive rates.
Frequently asked questions
Can I check a PDF for AI-generated text?
Yes. Upload the PDF to an AI detector with document support — aidetectors.io reads PDF and DOCX files directly, extracts the text, and returns an AI score with sentence-level highlighting. No copy-paste needed.
Is there a free AI detector for PDF files?
Yes — aidetectors.io lets you upload a PDF and scan it with a free account. The extraction and the detection both happen in one step.
Does AI detection work on scanned PDFs?
Only if the PDF contains selectable text. A scanned PDF is an image — run OCR first (most PDF apps and free OCR tools can do this), then upload or paste the recognized text into the detector.
Can I check a long PDF, like a thesis or report?
Yes, within word limits: free accounts scan up to 1,000 words per check and Pro extends this to 5,000 words per scan. For book-length documents, scan chapter by chapter — mixed human/AI documents benefit from section-level checks anyway.
How do teachers check student PDFs for AI?
Institutional tools like Turnitin accept document uploads inside the LMS, and for one-off checks teachers upload the PDF to a web detector or paste suspicious sections. Sentence-level results matter more than a single overall score.