I have a text file (ABCD.txt) which contains a number (456700010234) in it. 
The ABCD.txt file contains only the number (456700010234). Nothing else.

I want to display this number in one of the text boxes in C# form.
I prefer not to use a button. Just the textbox in the form/usercontrol.

If anytime I want to change the number, I will just update the text file (ABCD.txt) with a new number and thus, the new number will appear in the textbox automatically each time I open the form. This way, I won't have to re-program the software whenever the number changes. I just want to update the .txt file with a new number if the number changes.