Yes — adding comments to a PDF is one of the most widely supported PDF operations outside of Acrobat. Sticky note comments, text annotations, highlight comments with notes, and freehand drawing are all available in free tools across every platform. You likely already have what you need.
Adobe Reader (Free Version)
Adobe Reader — the free viewer, not the paid Acrobat — includes a full commenting toolbar. Sticky notes, highlights, underline, strikethrough, text boxes, and freehand drawing are all available. Open a PDF, click the Comment tool in the toolbar or go to Tools → Comment, and the annotation tools appear. Comments added in Reader are standard PDF annotations that any other viewer can display.
One historical limitation: older versions of Adobe Reader could only add comments to PDFs that had comment-enabling rights set by the creator. This restriction has been removed in recent versions — Reader can now add comments to any PDF regardless of permission settings.
Preview on Mac
Preview includes annotation tools through the Markup toolbar — click the pen icon in the top-right to reveal it. Available tools: text boxes (for adding typed notes), speech bubbles (popup comments), highlights, shape overlays (rectangles and ellipses for calling out areas), and freehand drawing. Preview's comments are saved as standard PDF annotations.
Preview doesn't support sticky note pop-ups — you can add text boxes and speech bubbles but not the floating note-style comments that Acrobat uses. For most annotation needs this is sufficient; for documents where the commenting system needs to match Acrobat's specific comment types, Preview has limitations.
Microsoft Edge (Built Into Windows)
Edge's built-in PDF viewer includes annotation support: highlight with color options, text notes, and freehand drawing with the stylus or mouse. Open a PDF in Edge, and annotation tools appear in the top toolbar. Annotations are saved when you save the file from Edge.
Edge's commenting is lighter than Acrobat or dedicated PDF tools — it covers basic review and markup needs but doesn't support all annotation types. For straightforward document review without installing anything on Windows, it's the most accessible option.
Browser-Based PDF Editors
Browser-based PDF Editor tools support annotation without any software installation. Upload the PDF, add comments using the annotation toolbar, and download the annotated version. These tools work on any device with a browser — Windows, Mac, Chromebook, iPad, Android tablet — which makes them useful when you're on unfamiliar hardware or a restricted device.
WukongPDF's editor includes text annotations, sticky notes, highlight, underline, and shape tools. Comments are embedded in the downloaded PDF as standard annotations visible in any PDF viewer. The browser-based approach is particularly practical for collaborative review where not everyone may have the same desktop tools installed.
Making Sure Comments Are Saved in the PDF
The key distinction: comments saved to the PDF file itself vs. comments that only exist in the viewer's memory. When you annotate in a browser PDF viewer and close the tab without downloading, the annotations are gone. Always download or save the annotated PDF before closing.
To verify that comments are properly embedded: save the annotated PDF, then open it in a different viewer — if the comments appear, they're embedded. If the file looks clean in a different viewer but showed annotations in the original, the annotations were display-only and weren't saved to the file.