If you mean highlighting it temporarily to select text for copying or something, yes, naturally, you can do it, as long as the pdf was created with text, not images. As long as the original pdf file has text data in it, not scanned images of the pages, you should be able to select the text. If the pdf has images, you might have to use OCR software like Abbyy(Google it), to extract whatever text possible from it.
If you want to give a permanent background color to text, I don’t think its possible in Adobe reader. You’ll have to try out an alternative pdf reader like Foxit (google it)