Notepad++ has a pre-installed plug-in called Converter that has a option to Convert ASCII to HEX and Vice-versa. This tool is quite useful as to convert data files that are in HEX format which are to be converted to ASCII to read.
How to Use it (Conversion Panel):
You can get to Converter Panel by going to Menu -> Plugins -> Converter -> Conversion Panel
You get a Dialog Box with ASCII, Decimal, Hexa-decimal, Binary, Octa-decimal fields. Entering a value in any of these fields converts text to other options.
You can convert the whole text file to ASCII from HEX and vise-versa by selecting all text in notepad++ and go-to Menu -> Plugins -> Converter -> ASCII to HEX/HEX to ASCII