Convert PDF to VDX

Although some websites claim that it is possible to convert PDF documents (probably with Visio diagrams) back to some of the Visio formats (.vdx, .vsd, .vsdx etc), pdf to vdx conversion seems to be highly unlikely.

At best, you could create a picture of the diagram and use it, but you won't get the Visio data back from PDF in the original format.

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