If you are in a Scene creating a PMI GD&T and get an error such as "Sorry, exception was catched for missing GDT file..." then it means you are missing some CAXA GD&T fonts from your C:\Windows\Fonts folder. Go to C:\Program Files\IronCAD\2018\bin\CAXADraft\Font and copy CXGDT.ttf and CXGDTSHP.ttf from there into C:\Windows\Fonts, restart IronCAD and try again.