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Name your thesis as UVA_year_familyname_givenname.pdf.
Creating a PDF/A file in Word for Mac OS X is not possible.
With free softwares, such as LibreOffice or Scribus, you can save as a PDF/A file.
With non-free softwares for handling PDF files, like Serif Labs Affinity Designer or Adobe Acrobat Pro, you can take advantage of free trials.
You can save as a PDF/A file by using Office Word for Windows on classroom computers and at Tritonia, but note that some settings might change, for example, line breaks can end up in a different place.
The computers in classrooms and at Tritonia also have the PDF-XChange software, with which you can convert a PDF file into a PDF/A file. https://uva.libguides.com/theses/PDF-A_XChange