What metadata usually leaks
Many PDFs carry an Info dictionary with fields such as title, author, subject, creator, producer, creation date, and modification date. Modern workflows may also embed XMP packets that contain richer XML metadata.
Why “save as PDF” is not enough
Re-exporting a file sometimes helps, but it can still preserve creator details, XMP packets, or inherited metadata fields. Basic online cleaners can also clear only obvious properties while leaving deeper XML traces intact.
A safer review workflow
Identify the document class, inspect properties, purge metadata locally, export a fresh copy, then validate. For sensitive material, local browser sanitization is preferable to uploading the PDF to a cloud scrubber.
Practical next step
If you already know you need a metadata wipe, use Remove Metadata from PDF. If the concern is specifically hidden XML packets, follow with Erase Hidden XMP Metadata.