Annotate PDF

How it works

Open the PDF, choose a tool and drag on the page: highlight, underline or strike out the text (you can also search for a phrase and mark one or all of the matches), write free text, stick a note, draw freehand or add a rectangle, an ellipse, a line or an arrow. You can pick the color, opacity, line width and font size, and move or resize what you placed before you apply.

The annotations the file already had (made here or with another program) appear in a list: for the usual kinds you can edit the comment, text, color or position, or delete them, in the same step. What this tool writes are standard PDF annotations, so any reader shows and edits them.

The annotations are added at the end of the file as an incremental update: the original content is not touched, and any signatures it already had stay valid for the version that was signed. Check the result in your usual PDF reader before you share it: the page tells you clearly what was done and what was not.

What is not preserved, and limits

• They are saved as an incremental update: the original bytes stay untouched and earlier signatures stay valid for the version that was signed, but readers report that the file changed after signing. If you do not want that notice, annotate before signing.
• A deleted or replaced annotation stays in the file history: the old bytes are still in the file. Annotating is not a way to remove content; to remove it for good use Redact PDF.
• Highlight, underline and strikeout need real text to select. A scan is a picture: there use free text and shapes, or run OCR first.
• Free text with letters outside the Latin set of the shipped font (Noto Sans) cannot be written: the page tells you which characters are missing and changes nothing. There is no glyph shaping or right-to-left layout.
• Rich text (bold, mixed fonts or colors) is not produced: each free text has a single font, size and color.
• Annotations of other kinds (links, form fields, stamps, attachments) can be listed but not edited; stamps and the like can be deleted, links cannot. Pop-up windows are not created.
• A password-protected PDF can be annotated (the page asks for the password and it is used only in your browser), but the result is saved WITHOUT a password. You can protect it again with Protect PDF.
• A file with a certification signature that forbids changes is not annotated: it is refused without touching anything, because adding annotations would break that signature.
• The result has been checked with pikepdf and qpdf (structure), poppler (pdftoppm, pdftotext), Ghostscript and pdfsig (signatures); it has not been tried in Adobe Acrobat or Reader.
• Readers differ in how they draw note icons on rotated pages: poppler always draws them upright, others turn them with the page.
• Everything happens in your device's memory and nothing leaves it. Very large files (more than about 100-150 MB in total) may fail, especially on phones; drawing and shapes are easier with a mouse or a pen.