Can I (Vietnamese) take visa into China by myself of my secretary can do it for me and what's the fee for F visa?

You can apply for the China F visa in person or ask your secretary to apply for China F visa on your behalf, the fee for single entry F visa is 30 US$, the fee for double entry F visa is 45 US$, the fee for multiple entry F visa valid for 6 months is 60 US$, the fee for multiple entry F visa valid for one year is 90 US$.

The regular processing time is 4 working days, if you want to get your visa within 2 working days, you also need to pay extra 30 us$, pay extra 20US$ for 3 working days processing.