We are writing a formal email and requesting the help from the reader. However we are not sure if it is correct to write "We would like to ask for your kind assistance to review the document". Is it to formal or even correct?
1. I would say "... assistance in reviewing this document." That sounds more natural in English.
2. I would remove the word "kind." Business English generally does not use phrases like this. I know they are common in other languages, so a sentence without them may seem harsh or rude to someone who would use them in his or her first language. In English, however, using them sounds too flowery.
I agree on both points. "Kind assistance" was a common phrase a very long time ago. And "your assistance to review" is incorrect. We can "ask you to review" or "ask for your help/assistance (in) reviewing".