Dear Sir or Madam,
I am writing this letter in order to invite you to attend the forthcoming graduation ceremony.
The ceremony will be hosted in the auditorium on our campus, at 10 o'clock in the morning on next Monday, January 15. It is advisable for you to dress formal. Please let us know your decision as soon as possible so that we could send you further details concerned. Since you are so popular among us that we sincerely hope you could accept this invitation and give the graduates a wonderful memory of our campus.
If you are available, we request the honor of your company. It will be highly appreciated if you could give us an earliest favorable reply.