How to make Sony Vegas Pro 13 work on a 4K display
There's apparently a hack which alters the Vegas executable to solve this problem. There's a setting of dpiAware in the application manifest which falsely tells Windows that Vegas is DPI aware and will scale up text and icons on a HiDPI display. Vegas does not do this. So, the value should be changed from true to false.

The hack tutorial alongwith link to required tool is available at https://www.youtube.com/watch?v=Vvr0c5VHGIM


                
            

I haven't needed to do this so I can't vouch for the method but it appears to work.