Cannot highlight contents of Text field

Hi,

I have Acrobat X Pro and am editing a document that contains a Text Field with several paragraphs of text. I want to highlight one paragraph one color, and another paragraph another color. I am not able to highlight anything within the Text Field. The highlighter tool does work on the Text Field Name but nowhere else. I can edit the font color, size, etc. of the text within the Text Field, but cannot use the highlighter.

The highlighter tool works fine in other PDFs that don't contain form fields.

Is there a way to highlight the contents of a Text Field or merge all the form fields into one, highlightable document?

Thanks,
Jason