the tax file should have a ".pdf" extension on it. If it has ".txt" then edit the name and change it to ".pdf" and open it with a PDF viewer. (or download the PDF file with a different browser...some "Edge"-browser downloads put the wrong file extension on the file)
IF the file has the extension ".tax2018" then you must have the desktop software installed to see what is in it.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*