Times New Roman PS

I am helping an author publish her eBook. She wrote a book in InDesign (16.1) using a Windows 10 computer. She exported her book as a PDF. We intend to distribute the eBook with Adobe DRM and Adobe Digital Editions (ADE). However, some Times New Roman PS characters in her eBook render with distortions — see the attached image of a sample of such distortions in the letter "p."

We have tried multiple InDesign export options, but we cannot resolve the font-distortion problem. Can someone point me in a direction to learn more and help her fix this problem in her eBook?