pdf to ppt. Text is not transferring over properly

Hi, when I convert my pdf files to ppt files some of the text is distorted. For example:

It should be: "Best practices to be considered"

Instead I get this: "Best prac4ces to be considered"

Or letters are missing in the ppt slides.

Any help would be greatly appreciated.
I am using the trial version Adobe Acrobat XI trial version and PowerPoint 2007