To start, click on the Annotate button and select a tool on the top toolbar.
It is also possible to select a tool by right-clicking on the word in the text. The pop-up menu will appear; here, you can find the highlight/underline/squiggly line and strikeout tools.
To remove an annotation, you can use the “undo” command (CMD+Z shortcut). Note that it is not possible to undo an action once the file is closed.