pdf to uml conversion is most likely searched by users that are looking for ways to recover or export UML diagrams from PDF documents, something that might not always be simple, especially since UML is no longer developed or actively supported.
You can use PDF tools to export the shapes/vectors of the diagrams and save these as SVG files for example, but recovering it back to the XML based UML diagram is unlikely, unless someone made dedicated utility exactly for this purpose - we do not know about any.
Updated: September 21, 2023