Open the PDF in a PDF editor or viewer with annotation tools
Select the text tool, comment tool, or fill-and-sign tool
Click or tap where you want to write
Type your text
Adjust font, size, color, and placement if needed
Save the edited PDF
If needed, use a digital pen or stylus to handwrite on the PDF
If the PDF is not editable, convert it to an editable format or use annotation mode
Export or download the final version after saving