Newbie question: Putting all occurrences of certain text string in a particular color

How can I change all occurrences of certain text string (say "software engineering") in a PDF in a particular color (e.g: red), and save the updated PDF.
I don't mean "highlighting" the text, but instead changing the actual color of the font (the ForeColor attribute).
Many thanks (sorry if this is an elementary question)

You can search for text within a PDF document, finding the coordinates of matching strings, as the following sample code demonstrates:

Once you’ve found the text’s location, you can change it as the following thread describes: