Admissions to an educational institution are usually confirmed by an invitation from the university or a letter of admission from the university admissions committee. This contains information about the university, the applicant, the faculty to which the student is admitted the estimated duration of the study, etc.
However, the invitation itself is not always a guarantee of automatic enrolment. Some universities send a conditional offer letter to the candidate first and later follow it up with an unconditional offer letter.
The university invite is a necessary document when applying for a student visa. Consulates accepts both originals and scanned/printed copies of the document and the letter can come as a hard copy in the mail or as a digital copy in the email or both.
As a rule, the document does not need to be notarized but it is worth confirming this with the consulate.