You can find these out of range characters and decide what to do with them.. Some of them may be curly quotes. You might just want to replace those with straight quotes. But others will be your nuisance characters that notepad might not handle well and you'd want to delete.
So for notepad++ a find of [\x{0080}-\x{FFFF}]
Note you'd click the replace tab so you can do find/replace..
The above should suffice, but some further explanation
The ascii range is 0000h-007Fh i.e. base10, 0-127. So if you search for any unicode outside that i.e. 128+ i.e. 80h-FFFFh then you can find those characters. Regex syntax has the concept of a character range so [A-Z] would be any character between A and Z in unicode. And in notepad++ you specify a character with utf-16 code with the notation of \x{...} where ... is the hex, so for 'A', whose hex is 41, you'd specify \x{0041}. Editpad would use \u....
e.g. \u0041
. So in editpad pro you'd do [\u0080-\uFFFF]
. In notepad++ you'd do as in the pic above. [\x{0080}-\x{FFFF}]
Notice the regex syntax aspect of it is the same, but the way a character is specified differs between text editors.