Requirements for someone using PR CARD

May I know which country you are from and what your purpose is to PRC? If you go there for sightseeing purpose, those documents are required: the completed application form attached with a passport-style recently-taken photo, your passport and copy of its data page, permanent residence card in Canada, round trip air tickets and accommodation booking record as well as other required documents. And then submit your application to the CVASC and apply for it.

I m a Nigerian living in Toronto and the purpose of going to PRC is visiting a friend and a factory

If so, I think a tourist L type is okay. The above-mentioned documents are enough. Of course, because you have a friend in PRC, you can ask her/him to write an invitation to you. In this case, you may not need to provide round trip air tickets and accommodation booking record anymore.