In Alibre Design 2018.0, we added an option for users to choose the PDF writer of their choice to use for 2D PDF Exports.
This new option can be selected from System Options>Drawings>PDF
If you install a new PDF writer (e.g. PDFill), it should show up here to be selected for use.
If you are unsure which PDF writer to get, we have a few recommendations of Free PDF writers listed below: