How to remove hidden data from a PDF: a step-by-step guide

Drop the PDFs anywhere on the page, or press Add files. Every file is read as it arrives: the file list says how many items each would lose, the header lists them by kind. Sanitizing changes nothing on the page - only what sits beside it in the file.

Each row is one kind, with the number the selected file holds. A lit row is removed, a dimmed one kept:

• Metadata - author, title, application, dates, XMP packets and application-private data, in the document and in its images;
• Attachments - files embedded in the PDF and attachment notes on the pages;
• Video, sound and 3D - embedded media with the files they play; browsers don't play them, but the file carries their weight;
• Scripts and actions - JavaScript, actions that run on opening or on a click, form-field scripts;
• Comments and markup - notes, highlights, stamps, drawings, with the reviewers' names;
• Page thumbnails - small renders of the pages stored in the file;
• Links and Form fields - off by default: links are navigation, and fields take what was typed into them along.

To keep what was typed into a form, Flatten PDF first: the values become part of the page, then the fields can go.

Press Sanitize PDF. The line under the button counts the items that go. The cleaned file is saved to your device at once - several files together as a ZIP - and the list says what was removed from each. What is removed is really gone: the file is rewritten, so no copy of it is left inside.

Not covered: text hidden under a box or in a hidden layer - that is what Redact PDF is for. Every saved file names MammothPDF as its producer.

Above the file list, Apply to decides how several files are cleaned. Under Selected file each file can have its own choices; under All files one set of choices is used for every file. Copy to the other files gives the choices on screen to the other files.

Without an account, and with a free one, you can sanitize two files in a run, each up to 15 MB. With Pro there is no limit on the number or the size, and you can save your choices as a preset.

• Black out names and numbers on the page? Redact PDF.
• Change some properties instead of removing them? Edit PDF metadata.
• Make the file smaller as well? Compress PDF.