C# ASP.Net: How to create popup window of text file

I have C# desktop application I'm converting to C# ASP.Net. It has some functions that output to text files. I already have a C# ASP.Net Default form that performs some functions with buttons and text boxes for output. I want to add more buttons for more functions and simply display the text file generated output from those functions in a popup window (I thought that would be easiest, since I have the desktop code that already does this). What's the best way to create and display popup windows for my text files, using buttons on my Default form? Any help would be greatly appreciated. Thanks in advance.