It is possible to highlight sections of a PDF without having the selected text added to comments that can be easily exported, as discussed in the Tip of the Night for March 1, 2019. In order for highlighted text to be added to comments, the option in Preferences in the Comments category, "Copy selected text into Highlight, Strikethrough, and Underline comment pop-ups" must be checked off.
Gilad D. has posted a script here which can be used to add highlighted text to comments. The batch version costs $60, but you can test out a free version. It will download as a file named, 'CopyTextsToHighlights-DEMO.jar'
The trial version will only process the first three highlights in any PDF.