A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
SVG is a relatively new format for Office. For backwards compatibility, Office programs create a fallback PNG of the SVG, and that's probably what you're seeing in the PDF.
You can try importing the SVG into the free programInkScape, then re-exporting. It has a couple of SVG export formats that might work better. If that doesn't help, use an EMF.