drop by stop by
Yesterday I stopped by your office to see you, but you were nit around.

Is this sentence natural and should I use the word drop by instead?

Question

drop by stop by
Yesterday I stopped by your office to see you, but you were nit around.

Is this sentence natural and should I use the word drop by instead?

Answer

'Stopped' and 'dropped' are both OK there. 'drop' can suggest a shorter visit, but apart from that they are interchangeable.
The only problem in your sentence is that you have 'nit' rather than 'not'.