Why Comments and Annotations in PDFs?
The ability to comment on PDFs is indispensable in many professional contexts: editors mark passages, lawyers leave notes on contract clauses, architects comment on plans, teachers annotate student work. And privately: when reading academic articles, working through manuals or preparing for exams.
The key advantage over printing and annotating by hand: digital comments can be deleted, searched, exported, filtered by author and forwarded by email, all without altering the original document.
The Most Important Annotation Types
Highlights
The most common annotation. Select the highlight mode, drag over a text range and the text is colour-coded. Default is yellow, but many tools allow different colours for different categories (red = critical, green = confirmed, blue = question).
Underline and Strikethrough
Underlining emphasises a text range. Strikethrough signals that a section is deleted or outdated. Both types are defined as separate annotation types in the PDF specification and are correctly displayed by all compatible viewers.
Sticky Notes
A small icon appears at the marked position. Clicking it opens a comment field with the full text. Sticky notes are ideal for longer explanations, questions or alternative suggestions. They occupy no space on the page and do not disrupt the readability of the original text.
Free Drawing
For plans, graphics and illustrations, free drawing is the most flexible option. Arrows, circles, lines and freehand annotations can be placed anywhere. This function is particularly valuable for technical documents.
Text Box
A text box is placed directly on the page, visible even without clicking. This is suited for short, immediately visible notes that should appear at a specific location.
Stamps
Standardised stamps such as Approved, Rejected, Revise, Draft or Confidential provide quick visual feedback without a lengthy comment text. Most tools offer standard stamps and allow custom stamps.
Edit and Annotate PDFs with the Edit Tool
With the PDF editing tool, you can add text boxes, highlights and annotations directly in the browser. This works on desktop and mobile devices, no software download required. The edited document is available as a new PDF for download.
Comments in Team Collaboration
In professional workflows, PDF comments are used as a coordination instrument. A contract is circulated to various stakeholders, each adds their annotations, and the result is a commented document summarising all feedback.
Important: when multiple people comment, author names should be correctly set so it is clear who left which comment. In Adobe Acrobat, comments can be filtered and exported by author, compatible tools work similarly.
Exporting and Summarising Comments
In professional PDF tools, all annotations can be exported as a separate comment list, as an FDF file or directly into a Word document. This is useful when proofreading notes need to be summarised or all feedback points listed in a report.
Important: Comments and the Original Document
Comments in PDFs are separate from the actual page. They are stored as an additional layer. The original document remains unchanged. If you want to share a PDF without comments, you can either create a copy or selectively remove the annotations.
Confidential comments should be removed before forwarding, just as hidden metadata should be. The redaction feature helps permanently remove unwanted content.
Annotating on a Smartphone
On a smartphone, highlights and sticky notes can be set with a finger. For free drawing, a stylus is recommended, as precise placement with a finger on a small display quickly leads to imprecise results. Browser-based tools are well usable in modern mobile browsers.
Conclusion
Comments and annotations make PDFs into living working documents. Whether for proofreading, teamwork, personal notes or formal feedback, the possibilities are extensive and suited to virtually every use case. Anyone who knows the different annotation types and uses them deliberately saves time and communicates more precisely than with separate emails or phone calls.