PDF 1.4 Password hash cracking

[Sheldor]

Hi,
I lost a Password of a important PDF file.
At the moment I am trying to recover the Password with this Parameter:

cudaHashcat64.exe -m 10500 -a myHash.txt -a 3 ?b?b?b?b?b

I am not sure if the Parameter are so right.
The Password can be any characters  ans the password is 8-12 characters long.
My GPU is a GTX 970

Are the Parameter so fine?

Thank you