How to preserve image quality when saving PPT to PDF?

In power point 2013, on the first slide I have this picture in PNG

Aftering saving the PPT to PDF it becomes

As you can see the image has became blurry around the edges of the letters.

Now this is after I went into Options -> Advanced -> Do not compress image

Why does my picture become blurry? Is there anyway to preserve the quality of this picture?

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