Drop a PDF and see its edit history: whether it was changed after it was created, what software touched it, and (when the file still contains an earlier version of itself) exactly what changed. Everything runs on your device; the file is never uploaded.
When the file was created, when it was last saved, and the software that made it, laid out in order so you can see whether it changed after it was first created.
Many PDF editors append changes rather than rewrite the file, so an earlier version of the document is often still inside it. When one is found, it's rebuilt and shown next to the current version in a before/after view.
Numbers added in a stray font that appears nowhere else on the page, and text hidden under a covering box: both are recovered and shown to you.
The complete metadata table (title, author, the software that made it, creation and modified dates, and edit-history records) is included with every check, viewable and printable.
Compare the created and modified dates in the file's properties. If the file was last saved well after it was created, it was re-saved at least once. …or let the checker do it.
Check which software the file says produced it. A bank statement naming a photo editor is worth a closer look. …or let the checker do it.
Look for earlier versions saved inside the file. Many PDF editors append changes rather than rewrite the file, so the original is still in there. …or let the checker do it.
Look for text set in a font that appears nowhere else on the page. A single value in an odd font is a common sign something was added later. …or let the checker do it.
Check the file's edit-history records for editing software that appears after the document was supposedly finished. …or let the checker do it.
What none of these can do is prove a file was never edited, which is exactly what the next section is about.
Filling in a form, adding an e-signature, using "print to PDF", and re-saving a file through a scanner app are all edits. A PDF that has been through any of them will honestly show signs of modification, and none of that means anything is wrong with the document.
A clean result ("no signs of modification found") is not proof the file was never touched. A full re-save through many tools produces a single-version file with nothing left to find, and internal details can be edited or removed. It means the checks didn't find a sign, not that no edit ever happened.
Scanned PDFs show very little, because scanning flattens a document into an image and discards the edit history, the original software record, and the text layer the checks rely on. A print-then-scan erases that history the same way, so a scan showing "no signs" is expected, not reassuring.
Every edit report includes the complete metadata table (title, author, the software that made the file, its creation and modified dates, and any edit-history records), viewable and printable, without installing anything or uploading the file. It's a PDF metadata viewer and a PDF last-modified-date lookup as a built-in part of every check.