Search for a string in Preview
I've not found a way to get Preview to search for characters like # or +, but Skim, an alternative PDF viewer (homepage here), is a good replacement/addition to Preview and is able to search more specifically.

I've tested it and found it was able to find C++ (without needing any quotes/special options) without bringing up all C results.

It was also able to search specifically for accented characters (like é or ö) — though requires such characters to be accented in the search to find them (i.e. you can't search for blah and expect it to match bläh, nor vice versa). In Preview, either search will return matches for both accented and unaccented characters.