Use the original source file instead of a redacted copy
Check document metadata, version history, and revision history
Compare multiple copies or earlier drafts of the document
Inspect adjacent pages, headers, footers, and attachments
Copy the text and paste it into a plain-text editor to see if hidden text appears
Adjust zoom, contrast, and display settings to reveal faint overlays
Use OCR on scanned documents to extract visible underlying text
Open the file in a different viewer or PDF editor
Inspect the file structure for layered objects or annotations
Request an unredacted version from the document owner or publisher