So, currently Autodesk Vault is not supported for use on a 4K monitor. What!? Are you serious?
I just found this out yesterday and shook my head in disbelief. I had a client call me to let me know that they had just unboxed a new 4K monitor, and that Inventor looked great, AutoCAD too, but that Vault was rendered unreadable.
I quickly scurried and did a little digging. Yep, it’s true . . . Autodesk is aware of the issue and the resolve is under future consideration via the Autodesk Vault Idea Station. In the meantime, there is a workaround that seems to work pretty well.
On your 4K monitor, right-click on the Vault shortcut icon and select the compatibility tab. Then select the Change high DPI settings button.

On the next screen, select the checkbox under the High DPI scaling override. In the dropdown list, select System (Enhanced).

Click OK, then Apply and OK. You should now be able to see and to use Vault on your 4K monitor.