How to batch highlight (permanently) keywords on PDFs for free?

Question

Considering that:

1. I'm doing a Systematic Literature Review;
2. the relevant information is so much easier to find when the keywords I need are already permanently highlighted;
3. however, manually permanently highlighting keywords over dozens of PDFs is boring, time-consuming, and robotic;

Obs.: I'm talking about keywords' occurrence all over the article text, not just in the "keywords" section.

My questions are:

1. are there free software tools for doing batch permanent highlighting on PDFs?
2. if they do exist, can you please point me at least one of them?
3. if you can point me at least one of them, can you please write, or point me a how to tutorial on using the tool for batch permanently highlighting?

Answer 1

To batch highlight keywords permamently, Foxit PDF Reader can be used:

1. In menu, click Comment -> Search & Highlight:

2. Change destination to All PDF documents in and choose folder.
3. Choose Match any of the words or any suitable option.
4. Enter keywords.
5. Check Whole Words Only and Highlight All Text checkboxes.
6. Search
7. Check Check all and press the yellow highlight button:

8. There's no "save all" kind of button as far as I know, so the quickest way is to close Foxit and click Yes to confirm all saves, after you finish all the highlighting. Or you can change automatic file saving in File -> Preferences -> Documents to 1 minute. And of course you can review the files and close their tabs one by one.