Student or Learner
Teacher, I assume I can use either past or present perfect tense. Am I right?
We have received your letter of May 1, 2012 wherein you enclosed the information on your company.
We received your letter of May 1, 2012 wherein you enclosed the information on your company.
Since you are writing to them in response to the letter, it has relevance to the present situation, and therefore the present perfect is the better choice.
PS - Using words like "wherein" makes your writing seem stiff and overly formal. We received your letter with the information you provided on your company.
Also, put a comma after 2012.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.