Why Annotate PDFs Instead of Printing?

Printing a document just to highlight it and scan it back is slow, wasteful, and loses quality. Digital annotation is faster, searchable, and shareable — annotate a contract in seconds and email the marked-up version directly.

• Reviewing contracts — highlight key clauses, add sticky notes with questions for your lawyer
• Academic papers — highlight findings, annotate methodology sections, add margin notes
• Collaborative review — add comments for co-workers before sharing the PDF
• Student notes — highlight textbook PDFs and add notes without printing

Types of Annotations

• Highlight — select text and apply a colour overlay (yellow, green, pink)
• Sticky Note — click anywhere to add a comment bubble with your note text
• Underline — underline specific text for emphasis
• Freehand Draw — draw with a pen tool to circle, arrow, or sketch anything on the page

How PDF Annotations Work (Technical)

PDF annotations are stored as annotation dictionary objects in the PDF structure — separate from the page content. This means annotations can be added, modified, or removed without touching the original content. They're rendered as an overlay by any PDF viewer that supports the standard annotation spec (ISO 32000), which includes Adobe Acrobat, macOS Preview, Chrome, Firefox, and all modern mobile PDF apps.

SynthPDF vs. Adobe Acrobat for Annotation

Adobe Acrobat has more annotation types (stamps, callouts, measurement tools) and team collaboration features. SynthPDF covers the 4 annotation types used in 95% of everyday tasks — for free, in the browser, with no account required. For occasional document review and markup, SynthPDF is faster to reach and requires no subscription.