Comments, highlights and notes are annotations, a layer above the page. Whether they appear depends on the recipient's reader drawing that layer, and simple viewers often do not.
Two other causes are common: the markup was never saved into the file, or the recipient is viewing in a browser tab that shows page content only.
Review markup is the most collaborative thing that happens to a PDF and the format handles it least reliably, because annotations were designed as an optional overlay rather than as part of the document.
Why annotations are optional
A PDF page has content, drawn as part of the document, and it can have annotations sitting above it. Keeping them separate is what makes them removable without disturbing the page, and what lets a reader show or hide markup on demand.
The cost is that displaying them is a choice. Full readers make it. Lightweight viewers, some mobile apps, embedded previews in email clients and document management systems, and some print paths do not, or handle only a subset of annotation types.
- Simple mobile PDF viewersOften skipped
- Email client previewsUsually skipped
- Some browser viewersPartially drawn
- Document management previewsOften page only
- Printing without markup enabledExcluded
- Full desktop readersDrawn correctly
Was it saved into the file?
The first thing to rule out, because it is common and entirely invisible from your side.
Some readers hold annotations separately from the document until you explicitly save, and a few store them in their own local database rather than in the PDF at all. In that arrangement the markup is attached to your copy on your machine, and the file you send contains nothing. The document looks annotated to you indefinitely.
Some annotation types travel better than others
Not all markup is equally portable. The basic types defined early in the format's life are widely supported. Later and vendor-specific additions are not.
Widely supported types
- Highlights, underlines and strikethrough
- Sticky notes and text comments
- Freehand drawing and simple shapes
- Text boxes placed on the page
Often skipped or shown differently
- Comment replies and threaded discussions
- Review status markers such as accepted or rejected
- Vendor-specific stamps
- Audio and attachment annotations
Making markup travel
Three approaches, in increasing order of certainty.
Ask them to open it properly
Often the whole fix. If they are looking at an email preview or a mobile viewer, downloading the file and opening it in a full reader will show everything that is there.
Flatten the annotations into the page
This turns markup into ordinary page content, so every reader displays it. The comments stop being interactive, which is the trade: nobody can reply to them or resolve them afterwards.
Export a comment summary
Full readers can produce a separate document listing every comment with its page and author. Sending that alongside the PDF guarantees the substance arrives regardless of what software the recipient uses.
When they show but do not print
A variant with a specific cause. Several readers have a separate print setting controlling whether annotations are included in output, and the default is not always to include them.
In Adobe Reader this appears as a choice between printing the document and printing the document with markup. Choosing the first prints a clean page no matter how much markup is on screen. Flattening removes the distinction entirely, since there is nothing left to exclude.
A better review workflow
Much of this trouble comes from PDF being used as a collaboration format, which it was not designed to be.
Where the document originates in Word or Google Docs, reviewing there is materially better: tracked changes and comments are part of the document rather than an optional overlay, everyone sees the same thing, and threads work. Reserve PDF review for cases where the PDF genuinely is the artefact, such as a finished design or a document you did not author.
Flatten comments into the page
Annotations drawn in as page content, so every reader shows them. Nothing is uploaded.
Common questions
Making review markup travel.
01Why can the recipient not see my comments?
Annotations are a layer above the page, and whether they appear depends on the reader drawing that layer. Simple mobile viewers, email previews and some browser viewers show page content only, so the markup is present in the file and not displayed.
02How do I check my comments are actually in the file?
Save, close the document completely, and reopen it in a different application such as a browser. Some readers hold annotations separately or in their own local storage, so markup that looks saved may never have been written into the PDF.
03What is the most reliable way to send markup?
Flatten a copy so the annotations become ordinary page content, which every reader displays. Keep the unflattened original if the review is still active, since flattening removes the ability to reply or resolve.
04Why do my comment replies disappear?
Threaded replies are a later addition that many simple viewers do not implement. They often render the first comment alone, or nothing at all. The replies are in the file with no interface to show them.
05My comments show on screen but do not print. Why?
Most readers have a separate print setting for whether markup is included. Choose the option that prints the document with markup, or flatten the file so there is no separate layer to exclude.
06Is PDF a good format for document review?
Only when the PDF is genuinely the artefact. If the document originated in Word or Google Docs, reviewing there is better, because comments and tracked changes are part of the document rather than an optional overlay that may not be drawn.