There is a German embassy in Islamabad, here’s the website:
He can apply for a visa to get married in Germany. For this you will have to make an appointment to get married with your local registry office (Standesamt). I recommend you contact the Standesamt, outline your situation and request to register to marry (in German ‘Anmeldung zur Eheschließung’).
The Standesamt will generally need at least the following documents from both of you:
- Birth certificate
- Certificate of ability to marry (Ehefähigkeitszeugnis)
If, due to your situation, it is not possible for you to obtain the last item, you can ask for an exemption and/or provide an affidavit regarding your ability to marry.
Your partner will have to provide additional documents to the German embassy in order to receive a visa. The embassy in Islamabad does not provide information on this but here is the list from the German embassy in Ukraine. The process and required documentation should be largely the same in all embassies:
An important element is that you will have to provide a declaration of financial obligation (Verpflichtungserklärung) for the time your partner is in Germany before getting married. He will also have to show that he is able to support himself financially after the marriage.
Let us know if you have any more questions about this.