I misinterpreted your problem. I thought you wanted to open a file for use in your program. One possible solution (This may not be any good - I'd need to know what you wanted to do with the open document) would be to copy all the lines of data into an array, and then put the array data into a multi-line text box.

This will only work with a *.txt file, a Random mode file, or a plain text file that has been given a different file extension.

You'll need to be a bit more specific about what you want the document open for though.