"Please check it out'' as an expression it is indeed correct but it is rather informal. Check something out is more commonly used to say for example "check this girl/boy out" which means to take a look at someone with a more flirtarious way or it can be used to say to a friend or to a group of people "my New video in YouTube is uploaded. Check it out!!" If we consider the above we can understand is quite informal to use this expression but is Based on the relationship you have with the other person. It would be better if you said(as you mentioned) "Please take a look at this file" or "could you please take a look on this file?" I hope I helped you!!?