Symptoms

Though Save As PDF generates a PDF file, its formatting/style is completely off and it displays hidden fields and such. This happens in all our environments (DEV, TEST, and Production). 

Diagnoses

Try the following configurations/troubleshooting steps as per:

http://help.k2.com/kb001444
http://help.k2.com/kb001454

Resolution 

After changing the PDF Converter service instance to using the K2 Service account authentication this resolved the PDF CSS not being applied issue.