Please answer to this question. Thank you in advance.
Dear friends
is this phrase suitable in a formal letter? isn't such request rude?

Dear professor ...
I'm so grateful if your keep this manuscript to yourself until it can be published. In fact my next goal is to find and join a research group and I need this manuscript published for that.
Best wishes

Question

Please answer to this question. Thank you in advance.
Dear friends
 is this phrase suitable in a formal letter? isn't such request rude?

Dear professor ... 
I'm so grateful if your keep this manuscript to yourself until it can be published. In fact my next goal is to find and join a research group and I need this manuscript published for that.
Best wishes

Answer

This would be correct and formal:

I would be grateful if you did not share this manuscript with / forward this manuscript to anyone else until it can be published.

Your option was not rude.  "keep something to yourself" is informal, but not rude.

Answer

I would say:
Dear professor, 
I would be grateful if this manuscript is kept confidential until it can be published. In fact my next goal is to find and join a research group and I need this manuscript published for that.
Best wishes