Select "Tools" and then "Draw" in the toolbar.

Navigate to your content and start drawing by clicking and dragging.

You can change your color clicking the box in the toolbar and adjust the line thickness using the slider.

To delete, click the trash can icon, or right click and select "Clear All" to remove all drawings.

Draw is just one of the many powerful PDF editing features PDFfiller has to offer.

Learn more here: https://www.pdffiller.com/en/functionality/177-draw-lines-arrow-shape-in-inside-pdf-document-form-file-application-contract-agreement-certificate-license-permit-annotate-online-mac-windows