Erm.. there's no such thing as a "vector png." PNG, by nature, is a raster format.
I'll assume you are using Fireworks since that's the only place I've ever seen vectors exist in a png file. Fireworks will embed vector content within the png format, that's proprietary and non-standard.
What Fireworks basically does is save two versions of the file within the png container - the standard raster image used everywhere, then a hidden sub-layer of data which only Fireworks reads. That sub-layer of data can contain vector information, but again, only Fireworks reads it as far as I know.
Whether or not you can convert the PDF for use with Fireworks depends greatly upon how the PDF was saved and what application was used to create the PDF.
First thing to try, drag the PDF to Photoshop.....
If the PDF was saved via Photoshop with editing capabilities in tact, and vector and/or shape layers were used in the creation of the Photoshop file, you will see the vector and/or shape layers upon opening the PDF with Photoshop. Save the file as a .psd file. Open the .psd with Fireworks and be certain that "Maintain Layer Editability over Appearance" is selected. The vector data should transfer without any issues.
If the PDF shows no vector/shape layers when opened with Photoshop, do nothing and close the file.
Next thing to try, drag the PDF to Illustrator....
If you can select objects/paths in Illustrator, you may be able to do a bit of work to get the vectors to export to a .psd file which can then be opened in Fireworks with the vector data.
How you do this greatly depends upon the actual artwork and how it was originally constructed. If it was originally built with Illustrator or Indesign, it may take very little effort to export to a .psd format. If it was built in some third party app it may not translate well to a psd and may take some effort to re-fill or re-color elements and remove raster images and/or clipping masks which can be created at times.
There are occasions where you have all the vector paths, but they have been converted to clipping masks with embedded raster images for fills. Often you need to remove the raster fills and convert the clipping paths to standard paths then recolor everything. Once all that is done, you can often choose File > Export > PSD and choose to "write layers" and get decent results. That resulting .psd file should work in Fireworks just like any other .psd.
If dragging the PDF to either Photoshop or Illustrator does not result in any paths or vector data indicators (anchors, beziers, etc) then there is no vector data contained within the PDF.
In the end.... there are dozens of ways to create a PDF. There's no blanket "yes" or "no" answer... the best I can say is "it depends upon the PDF."