Almost every modern tax preparation and accounting software has default PDF export function as standard function, so it shouldn't be difficult to export .t18 tax return files as .pdf documents, i.e. achieve t18 to pdf conversion. Just keep in mind that exporting to PDF is usually done only for viewing or printing purposes.
Any version of H&R Block Tax Software above 2018 should have all you need to convert t18 to pdf. Some third party tax preparation tools may also support H&R Block files and allow import of historic data.Open T18 file Open PDF file
A tax preparation software
A Mac version of popular tax software