The United States of America are a contracting state of the Hague Convention Abolishing the Requirement of Legalisation for Foreign Public Documents. Therefore, documents issued in the United States of America should in principle be certified by means of an apostille in order to be recognized in Austria.
However, TU Graz can also accept documents if the issuing institution (school or university) sends them directly to TU Graz. This applies for example to high-school transcripts, SAT, ACT or AP results, transcripts from universities, certificates of completed courses, etc.
The required documents should be sent by the issuing institution directly to the TU Graz Registrar's Office.
If there are documents that cannot be issued in multiple copies by schools or universities (e.g. high-school diplomas, degree certificates) and therefore cannot be sent by them directly to TU Graz, then you must bring these documents in the originals to the Registrar's Office of TU Graz.