Hire a programmer to write an application for you. Or learn little bit about "sed" command-line utility and how to install it under Windows (warning: this is not point-and-click task!!!)
If you are under windows, install cygwin: https/www.cygwin.com/
Then open up the cygwin terminal and use the following command:
Code:
for f in *.txt; do sed 's/[^[:alnum:]]//g' "$f"; done
This loops through all files with a .txt extension in the current directory and deletes all non-alphanumeric characters. If you want to preserve whitespace as well:
Code:
for f in *.txt; do sed 's/[^[:alnum:][:space:]]//g' "$f"; done