What is Government invitation? Is it mandatory for L type VISA?

I am starting to work with Beijing Huahuan Electronics Co.Ltd. My company HQ wants me to
visit Beijing for Training. What document I required to submit? As a Bangladeshi passport holder, I went to Embassy in Bangladesh today. They inform me I require-

1. China Government Invitation Latter

2. Company Invitation Latter

From where I will collect the China Government Invitation Latter and from which department. In that situation my company will arrange China Government Invitation Latter but they are not sure from which department they will collect it form. Can you please help me on it.

Thanks & Regards

Asif