Is this WinForms or WPF?
Also unless you do some surgery on config files, the CLR will limit your objects to being a max of 2GB in memory.
Best solution either way will be to display the file in chunks.
The process might look something like this:
Read lines 1-10 of file.
On scroll down, display lines 2-11 of the file.
Be careful of only keeping the lines that are being displayed in your array of lines, otherwise this will lead to a huge memory leak since we're not cleaning up the lines we're not showing and essentially loading in past that 2GB anyways. You can either set the string to null to trigger the garbage collector, or overwrite it in something like an array of strings with 10 elements.
For some reason, some Amazon reviews said it was a scam 'cause it launch there before they made an official launch on their webpage...anyway, according to people, it's good...it was gonna be my first option to buy when I wanted something to farm in games automatically, but then I backed down since tax fees and shipping would have costed me a fortune to Mexico...