Converting study visa into Z type

You should first prepare those documents: your passport, a completed application form, a recently-taken bareheaded color photo, valid registration form of temporary residence, alien employment permit, and an invitation letter from a duly authorized unit (your employer will get the last two documents for you). Next, go to the exit and entry administration of the local PSB to convert the student X type to a work Z type.
The work Z type cannot be based on marriage certificate or anything else.