What hidden data can a PDF contain?

By Check Before Send · Updated 13 October 2026

Quite a lot. Beyond the words on the page, a PDF can carry document details such as author and title, comments and markup, attached files, filled-in form values, scripts, and earlier saved versions of the file. None of these is visible when you read the page.

This guide lists what we found in test PDFs, one kind per file, what the PDF standard says about two of them, and what the checker left in place on purpose.

What the standard says

The PDF standard defines a document information dictionary with entries for title, author, subject, keywords, the program that created the document, the program that made the PDF, and two dates. It defines the author as the name of the person who created the document.

It also defines annotations, which is how comments live in a PDF. A text annotation is a sticky note attached to a point in the document: closed, it shows as an icon, and opened, it shows a pop-up with the text of the note. The note's text is stored in the file whether or not anyone opens it.

What we found in test PDFs

We made small test PDFs with invented content, one kind of hidden data in each, and ran Check Before Send on them.

Test file	What the tool listed
Document details	Author, title, subject, keywords, the creating program and two dates
Comments and markup	A comment, a highlight and an ink mark, with the reviewer's name and the note text; a phone number inside a note was found as a separate finding
Attached files	Two attached files, one on a page and one on the document, with names and sizes
Filled-in form	The values typed into three form fields, and an email address in one of them
Scripts	JavaScript that runs when a page or the document opens, and a link that launches a file
Earlier saves	A second, earlier version of the file that still held an email address
Links	A link to a website, listed and kept

For each of the first six we let the tool make a copy, and then scanned the copy a second time. In four of them, nothing was left. In the scripts test, only a website link remained, because links are kept by default. In the form test, an email address in a field was replaced with a marker, while the form values and the editable fields were still listed as present, because the tool does not remove those unless you choose to.

What this means

Hidden data is not one thing. A check that looks only at the author misses the rest.
Some items are kept by default because removing them changes what the file does: links and editable form fields. The tool lists them so the choice is yours.
A comment can hold personal information of its own, such as a phone number, so it is worth reading, not just deleting.

Limits

These are small synthetic files made for testing. Real PDFs from other programs can store things in other places. A PDF can also be made of page pictures; Check Before Send reads those with text recognition, which can misread, and never reports them as fully checked. Apple's guide notes that annotations stay editable unless you flatten them when you save, so the way a PDF was saved matters too.

Check the PDF before you send it

Drop the PDF into Check Before Send. It lists each kind of hidden data it finds with the values shown, you choose what to remove, and it writes a new copy and runs a second scan on that copy. "Verified not found" means that second scan found nothing, not that the file is guaranteed clean.

The file is read inside your browser and is not uploaded; the Trust Center explains how to confirm that. For one common case, see where the author name in a PDF comes from, or browse the other guides.

Sources

More guides

Are comments in a PDF visible to others?Yes, if the comments are still in the file you send. Each note, the reviewer name and any highlights are stored in the PDF. What we found in a test file and how to check.
Are resolved comments still in a Word document?Yes, in our test a resolved comment stayed in the file with its text and author, and accepting every change did not remove it. What stays, and how to check.
Can someone see when I took a photo?Often yes. The capture date and time are saved inside the photo file. What the EXIF tags hold, what Apple says travels with a shared photo, and how to check a copy.
Do you need to blur license plates in a video?It depends on where the video goes. What the EU data board and the UK regulator say about plates and blurring, and what our detector found and missed on real clips.
Does a black box hide text in a PDF?Usually not. A black rectangle only covers text, and the words can still be copied out. What the PDF standard says redaction must do and what we saw in a test file.
Does a photo file store my name?It can, in more than one place. Where a photo file keeps an author name, what the IPTC and XMP standards add, and what we found in test photos.
Does a video file carry location and date?Yes, a phone video can store where and when it was recorded, the device, and names or comments. What we found in test videos and how to remove it without re-encoding.
Does black or white text hide words in Word?Black shading, black text or white text hide words from the eye, not from the file. What we found in a test document and what Microsoft says its inspector cannot detect.
Does Google Photos remove a photo's location?Not always. Google says it cannot edit a location your camera saved, and edits do not follow a file you download. What that means and how to check the copy you send.
Does removing photo metadata change the picture?In our tests the decoded pixels were identical after metadata was removed from JPEG test photos. What stays on purpose, such as orientation, and what to look for.
Does saving a Word file as PDF remove comments?It depends on two Word settings. What a PDF kept in our test of comments, tracked changes and author details, and what to look at before you send one.
Is blurring a face in a video enough?Only if every frame is covered and the original is not sent. What YouTube, the UK regulator and the EU data board say about blurring, and what our own tests missed.
Is EXIF the only hidden data in a photo?No. A JPEG can also hold XMP, IPTC and comment blocks, and some segments no tool can read. What each one is and what we found in test photos.
What does a screen recording capture?Everything on screen while it runs, plus sound if you turn it on. What Apple documents for iPhone, and how well our tool found invented emails, phone numbers and codes.
What does Word's remove-personal-information do?Word can strip names from a file on save. In our test it blanked author and company, but the comment text and tracked change stayed. What it removes and what it leaves.
What is EXIF data in a photo?EXIF is the information a camera writes into a photo file, such as time, device and sometimes GPS. What the tag list contains and what we found in test photos.
What is inside a Word .docx file?A .docx is a zip of XML parts and your text is only one. What a small test file held, from comments to reviewer lists, and what the Microsoft inspector covers.
What personal information shows up in a video?Faces, plates and on-screen text, but also voices and the file's own details. What regulators say counts, what our detectors look for, and what they never see.
What to check in a photo before you post itTwo places give a photo away: the data stored in the file and what the picture shows. What Apple and Google document, and what a tool can and cannot see.
Where does a PDF's author name come from?A PDF can name its author even if you never typed one. What the PDF standard says, what Word did in our test, and how to leave the name out before you send.
Do iPhone photos have location data?Often yes. Here is where an iPhone gets a photo's location, what else the file carries, Apple's three ways to leave it out, and how to check a photo before you send it.
How to see who last edited a Word documentWhere Word shows who last edited a file and when, what the file stores about its author, and how to remove those names before you send it to someone else.
Why can't I see tracked changes in Word?When Word shows a clean page, the changes are usually only hidden. Check the four settings that control what you see, and why hidden is not the same as removed.