I just played with this with NVDA a short while ago, and again with NVDA off.
NVDA is using Word's own search via the Navigation pane that opens when you hit CTRL+F or NVDA+CTRL+F. When the search is done, focus is sitting on the "Next Result" button, and each activation moves you from the currently focused occurrence of the found word/phrase to the next, highlights are unaffected other than the one that indicates actual current focus moving from one occurrence to the next. If I hit ESCape once I've arrived at the occurrence I'm interested in, focus jumps back in to the document itself and that instance is selected. If I then right arrow or left arrow it removes selection if that's what one wants to do, or if I start typing it replaces that instance with whatever I type, which is standard behavior.
As far as PDF files go, much depends on the actual PDF reader being used, so it is vital to know that.
Brian - Windows 10 Pro, 64-Bit, Version 1809, Build 17763
Growth for the sake of growth is the ideology of the cancer cell.
~ Edward Abbey