iSkysoft PDF Editor 6 Professional for Mac allows you to add text markups, freehand drawing, sticky notes, and more to PDF files.

Highlight PDF Text: Open the PDF file with the program, and click on the "Comment" > "Hightlight". And select the texts in PDF file, the texts will be highlighted. And you are able to choose the highlight color and opacity.

Underline PDF Text: First open your PDF with the PDF editor, and click the "Underline" button under the "Comment" menu. And then select the texts in PDF, and you will underline the texts.

Strikethrough PDF Text: You can click on the "Strikethrough" button under the "Comment" tab, and select the texts to strikethrough the texts in PDF.

After you open the PDF file with the program, go to get the comment tools under the "Comment" menu. You can click on the "Text Box" button and input the texts to annotate the PDF. And you can click on the "Text Comment" or "Text Callout" to indicate specific information on the PDF file.

Click on "More" under the "Comment" tab, you can get options of "Sticky Note". The "Sticky Note" feature allows you to leave comments to PDF file.

You can annotate PDF by adding freehand drawing and shapes, including Arrow, Rectangle, Polygon, Line, Connected Lines, Oval, Squiggly Line, Pencil, and more.