Is the PNG at 200 ppi or more, a scan of a clean white paper original (not photocopy or fax) with text in paragraphs of common English?
The image format doesn't matter. What matters is the resolution of the image (the higher the better) and the quality of the scan and the text in it.
Found out the hard way. It can't OCR white text on a black background. I inverted the image in photoshop and job done, Acrobat recognised the text!!
Thanks for the posted answers.
Acrobat's OCR is pretty good, but no match for dedicated OCR applications. For more challenging OCR jobs (like your's, or two different languages in the same document), I keep a dedicated OCR application around. It's a bit more cumbersome to use vs. just clicking the "recognize text in this file" tool, but when needed, it does a better job.