When using PrintDocument class for printing on vb.net, It won’t allow you to change
In order to set those values manually, first, you need to define a custom paper size using the code below. Then, you can set it to PrintDocument’s PaperSize property:
Dim csz As New System.Drawing.Printing.PaperSize("Custom Paper Size", 800, 600)
PrintDocument1.PrinterSettings.DefaultPageSettings.PaperSize = csz
I hope this helps you with your programming, Cheers!