Regarding visa/residence permit

• I need a document stating the provisional end of my studies (confirmation for submission to immigration authorities). Where can I get such a document?
• I was admitted to my master’s program with the condition to submit my official bachelor’s certificate within one year, but I won’t be able to meet this deadline. What should I do?
• I came to Germany with a study visa, now I have a residence permit for study purposes. What does this mean for me?
• What happens with my visa when I graduate?
• I have admission to the master’s program but the waiting period for my visa is very long. What should I do?
• Can I stay enrolled for 1 or 2 more semesters after I have graduated?