Jay C. answered 07/08/19
Graphic Designer with 20+ years Experience using Illustrator
If I am understanding this correctly it should be really simple. An AI file is essentially identical to a PDF! Just open with Illustrator and Save As... PDF.
If you don't have Illustrator you can use your printer's driver. Just right-click on the AI file and choose Print. Then instead of printing it to paper just use the Print to PDF function and it will save it as a PDF.