Latest Microsoft Visio has native support for PDF format, so it's the clear choice here for vsdx to pdf conversion. Except for that, it is likely that you can also find several other programs capable of Visio export, although these might not support the latest version of the format. Some kind of Visio viewer with print support might be enough for PDF export purpose, you would just have to use virtual PDF printer.
Open VSDX file Open PDF fileA diagramming program for Apple Mac and Windows
A Visio viewer for Mac