Dear Great Man,
Welcome back to the Wefugees Community and thank you for your question.
A "Duldung" is a "temporary suspension of the deportation" and not a residence permit. Holding a Duldung, people are unfortunately not allowed to leave Germany. In many cases, people receive a Duldung because they can not provide a passport. Without a passport it is very difficult for the authorities to deport people to their country of origin.
I am not aware of cases, in which the immigration offices gave a permition to a Duldung holder to travel to another country in order to apply for a passport. Depending on the individual situation and the actual reasons which prevent the deportation for the time being, you may also be at risk for deportation as soon as you hold a valid travel document.
I will also link our dear @alla_fka here. Maybe she can add some legal details or correct me.
In any case, please don't hesitate to get back to us with any further questions.
All the best,