Registering in Paderborn
The city offices in Paderborn are located in "Am Abdinghof" which is right in the very centre of the city.
To register, you need to go to the Einwohneramt. This is very easy to find. The actual building is very large and occupies most of one side of the street. Once you are inside, you will see big signs with huge arrows indicating the direction to the Einwohneramt.
They have some staff here who speak English but you may need to wait for them. If you can get by in German, you will rarely have to wait for more than a minute or two.
The last time that I went, it was in the middle of the carnival season and I spoke to a charming middle aged lady who was wearing a sailor suit and who had dyed her har and eyebrows bright blue!
The folks there are all very friendly and efficient. They will register you, but they cannot issue you with an Aufenhaltserlaubnis. For that, you must go to another office in the same building but, the staff will give you directions to it. When I went there, I was dealt with by a man who was a complete contrast to the folks in the Einwohneramt. Surly, abrupt and rude would be a fair description but perhaps it was my fault as I arrived in his office while he was in the middle of a private phone call to a friend.