How to reload and modifies files without regular open close?

I am writing code to write data in file (file may be any file like outlook/word/excel/txt etc. whichever open ) . My code write input text to a file when method calls, and i need to write this input at desired file which would be browsed or by giving path in code. Currently I need to open close file everytime to watch updated file , but I want to open file in taskbar and it will update automatically . How to do that ?

Thank you.