What is the list of documents do I need for visiting a friend in China for a week?

No, you can provide an invitation letter from your friend as well as copies of their passport and residence permit instead. The letter should include:
(1) Information on the applicant (full name, gender, date of birth, etc.)
(2) Information on the planned visit (arrival and departure dates, place(s) to be visited, etc.)
(3) Information on the inviting entity or individual (name, contact telephone number, address, official stamp, signature of the legal representative or the inviting individual)
Besides, a round-trip ticket is necessary apart from general requirements: passport, application form with photo.