After you could find a supervisor and agree upon the supervision of your doctoral project you should check the doctoral regulations of your faculty if you should sign a supervision agreement.

After you agreed upon supervision you need to submit an application to the dean's office of your faculty to be accepted as doctoral researcher. The faculty will send a formal acceptance letter in return confirming that you fulfill all formal requirements - or in exeptional cases should fulfill additional requirements. You will find all details about your application to the faculty and the required documents in the doctoral regulations.

After you got the formal acceptance letter of your faculty, you are eligible to enrol as doctoral researcher.