Example: I am using a dictionary application "WordWebPro". This app sits in a system tray waiting for me to select a text (typically a word) in any application (except edits on html forms) and to hit a hot key. It then wakes up with the selected text copied into its own edit. If the selected text comes from an application like Word, Notepad or an edit component I can make a correction and the corrected text replaces the original text.
So, how does one go about doing the same thing?