To add an annotation in PDF, upload your document to pdfFiller, or choose the document your want to annotate in “My Forms” page and click “Fill” button. You can highlight text or add comments, sticky notes or underlines in your PDF document, application form, license form, contract document or certificate file online. Open “Draw” tab and access the editor toolbar, you can have a variety of annotation features: highlight text, add comments, underline text and insert sticky notes or arrows.