The personal invitation from a friend doesn't require any seal or stamp, it should be written in first person, the invitation letter should include the below contents:

1. the invitee's personal information (full name, passport number, employing company and position)
2. the relationship between invitor and invitee
3. purpose of invitation (travel in China together)
4. travel arrangements (enter date, exit date, where will you visit)
5. who will pay for the travel
6. promise that the invitee will abide by China law and exit China on time
7. inviter's personal information (full name, China Id card number or passport number, email, telephone number, mobile phone number) if the invitor is foreign national, photocopy of China residence permit and his passport are required.
8. the signature of inviter