I saw a thread to convert Docx to a mobi file you must first convert it to pdf.
So went to preference's and changed my output to pdf, I highlighted the books and then Calibre crashed. So restarted it and now every time I hit the output button it crashes. I can hit the input button and make changes but touching the output button is the kiss of death

So I went and downloaded Calibre again and hit repair and it still crashes when I hit the output button. I have tried running the wizard again as well.
Problem signature:
Problem Event Name: APPCRASH
Application Name: calibre.exe
Application Version: 0.8.31.0
Application Timestamp: 4eeac627
Fault Module Name: QtGui4.dll
Fault Module Version: 4.7.3.0
Fault Module Timestamp: 4dec4b47
Exception Code: c00000fd
Exception Offset: 004a7387