Convert PDF to VSDX

Although some websites claim that it is possible to convert PDF documents (probably with Visio diagrams) back to Visio's VSD format, it is highly unlikely. What these sites usually offer is but an export to some graphics format (like JPEG or PNG)  which you can then import to Visio as object. At best, you could create a picture of the diagram and use it, but you won't get the Visio data back from PDF. Some third party MS Office alternatives might also be of help, but these might not always support the latest version of Visio formats.

Simply put, it is impossible to convert PDF to VSDX directly.
Thus, there is no so-called pdf to vsdx converter or a free online .pdf to .vsdx converter to be found.