extension of visa for 25 days

Nazir, you need to extend it 7 days earlier before it expires at the exit and entry administration of the local PSB after you enter PRC. The required documents for M type extension contain your passport, the application form, a passport-style photo, valid registration form of temporary residence, and an invitation letter from your business partner. But I’m afraid the extended date cannot be 25 days because usually, the extended days cannot be more than original stay duration.

thank you , but is it the same invitation letter , i mean confirmation of invitation , like they sand me for the embassy of PRC? and can I extend my stay in every province ?

Nazir, I’m afraid you need to get a new invitation from them.
You should extend it at the PSB in the area you live.