Actually, it’s not so hard to

Actually, it’s not so hard to get the clues. The basic reason is that MOV container files can contain data encoded using various compression and encoding schemes. Premiere Pro can import the MOV container files, but the ability to import the data that they contain is dependent on the codecs (specifically, decoders) installed. Therefore, the quick solution is to convert your QuickTime MOV video files with the proper codec before playing it with Adobe Premiere.

http://tips-on-avchd-video-issues.over-blog.com/2015/10/edit-mov-videos-in-premiere-without-issue.html