How it works
Objects on top of the page
Open a PDF and each page is drawn in your browser. Everything you add is an object laid over the page: text, a whiteout box, a highlight, a picture or a signature. Pick a tool, click or drag on the page, then drag the object to move it or pull its corner handle to resize it. Arrow keys nudge a focused object by one point, and Shift makes it ten.
Nothing in the original page is deleted. Whiteout paints a white rectangle over what was there, so the old text can still be found underneath by a program that reads the file. Use it to hide marks on paper, not to redact secrets.
Writing the edits into the file
Download writes each object into the page with pdf-lib. Whiteouts and highlights go first, then pictures, signatures and text, so writing always sits on top. Highlights are blended with the page like a marker, so the text below stays readable. The page's own content is wrapped first so its rotation and settings cannot disturb your objects.
Text uses a standard PDF font (Helvetica, Times or Courier). A line with characters those fonts lack, such as Vietnamese letters, is drawn as a sharp image of the text instead, so it looks right but cannot be selected afterwards.
position (pt) = pixel on screen ÷ (screen width of page ÷ page width in points)
Signatures
Draw on the pad with a pen, finger or mouse. The strokes are smoothed and saved as a vector shape, cropped to the ink, then placed on the page as an object you can move and resize.
