A professor has only proofread my paper. Should I include him as author?
I would thank him in the acknowledgments. Although there is no set standard for what is required to be an author, it is generally accepted that they must make a research contribution. Proofreading definitely doesn't meet that criterion (or any of the other criteria that I have seen).

I did this in one of my recent papers. I just said: 


  We would also like to thank Bob Bob for his helpful feedback on a draft of the paper.