Is it acceptable to ask a professor who is not your supervisor to provide comments on your thesis draft? I want my thesis to be the best it possibly can be. My supervisor is away for one month right before my thesis submission. Is it inappropriate or poor etiquette to ask another professor in the field who has shown interest in the topic to read the paper and offer any suggestions? This other professor teaches at a different institution, and will not be part of the panel or defence process.
If you have an existing relationship with this professor, you could ask, but be prepared to hear "sorry, I don't have time".

If this professor is a stranger to you, this is probably an unreasonable request.