How to remove comments and annotations from a PDF properly

The short answer

To remove comments from a PDF, delete the annotation objects themselves, not just the visible notes. Sticky notes, their popups, replies, highlights and drawn markup are each separate objects attached to the page. A tool that deletes annotations by category removes all of them, along with the author names and timestamps they carry.

The reason this needs saying is that a PDF's review layer is much larger than what you see on screen, and several common ways of getting rid of it leave most of it behind.

Annotations are not page content

A PDF page has two layers. The page content is the text, images and drawing that make up the document itself. Annotations sit above it as separate objects, each listed against the page it belongs to and each with its own type: a sticky note, a highlight, an ink stroke, a stamp, a link, a form field.

Every comment-like annotation carries more than its text. It records an author name, usually a creation and modification time, often a subject line, and frequently a pointer to a popup annotation that holds the same text again for display. A reply is its own annotation, pointing back to the one it answers. Twelve visible comments can easily be forty objects.

That separation is what makes clean removal possible: because the comments were never part of the page, taking them away restores the page exactly as it was before anyone marked it up.

What "delete comment" often leaves behind

Deleting comments one at a time in a viewer, or ticking hide, can miss more than you would think.

• Replies. Deleting a parent note in some viewers leaves its replies in the file, attached to nothing visible.
• Popups. The popup that displays a note's text is a second object. If the note is removed but the popup is not, the text and author name remain.
• Hidden and collapsed annotations. An annotation marked hidden, or a resolved comment collapsed out of the list, is still present and still readable in a different viewer.
• Stamps and drawings. Approved, Draft and Confidential stamps, arrows and freehand ink are annotations too, but they are often not shown in the comments list, so a reviewer clearing comments does not see them.
• Earlier revisions. Many editors save by appending changes to the end of the file rather than rewriting it. A comment deleted in such a save can still be sitting in the earlier revision inside the same file.
• Document metadata. Removing every annotation does nothing to the Author field and dates in the document's own metadata, which may name the same reviewer.

Removing annotations properly

World of PDF's Remove PDF Annotations tool reads every annotation on every page, groups them by what they are, and shows a count for each group before anything is removed. Comments and notes covers sticky notes, text boxes, popups and insertion marks; highlights and text markup covers highlighting, underlines, squiggles and strikethrough; drawings and stamps covers ink, shapes, lines and stamps. Those three are ticked by default. Links, attached files and form fields are listed separately and left unticked, because removing them changes what the document does rather than just cleaning it up.

Two details make the removal thorough rather than cosmetic. When an annotation is removed, the popup it points to goes with it, even if that popup is not listed on the page. And the removed objects are deleted from the file, not merely unhooked from the page, so the comment text and author names cannot be found by opening the file in a text editor. Anything of a type that fits no category is counted under Other, so nothing is invisible.

A note on signatures: a hand-drawn signature added as ink markup is an annotation in the drawings group. Untick that group if the signature should stay.

When flattening is the wrong tool

Flattening and removal are frequently confused, and they do nearly opposite things. Flattening keeps how an annotation looks and paints it permanently into the page, discarding only the interactivity. Applied to review comments, it would ship every highlight and sticky-note icon baked into the document where nobody can remove them.

World of PDF's Flatten PDF tool targets form fields specifically and leaves comments and markup alone, so it will not do this by accident. But other software that flattens everything will, and the result cannot be undone.

Flattening is right when markup is meant to stay: a signed form, an approval stamp that must not be dragged away. Removal is right when the markup is internal and the document is leaving.

When markup will not come off

If a removal tool finds no annotations but you can clearly see highlighting or handwriting, that markup is already part of the page content. Someone flattened it, printed and rescanned it, or exported the file in a way that merged the layers. At that point it is no different from anything else drawn on the page, and the only way to get rid of it is to cover it, which also covers what is underneath.

Before sending, finish with a metadata check. The Privacy Risk Scanner lists the Author, the creating and producing programs and the dates the document carries, and can strip them, which closes the gap that annotation removal leaves.

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