unable to open PDF version 1.7 files on my Mac

I have been having problems with (opening/viewing/printing) PDF files which a website has produced with Acrobat in version 1.7 type PDF's. The website owner says that this is a problem with Macs because of Preview not supporting the newer format of PDF's, which I had not heard about until I downloaded some PDF's he has on the site. He tells me that his Windows PC users are able to open and print these newer version PDF's, and that I just need a reader that only tries to view the file. However, I have tried Preview, Graphic Converter, and a few other programs which are supposed to be able to open PDF files. (In the case of Graphic Converter, these PDF's that the website has (but apparently he has some PDF's which were encoded with an earlier version of the Acrobat on his Windows PC, and some of the PDF's I can open in Preview and other programs, so it's mainly occurring with the more recently encoded PDF's, where he used a newer version of Acrobat to encode them in version 1.7+. 😠

Has anyone else run into this problem with opening/viewing/printing PDF's which were encoded on a PC with the newer version of Acrobat? Quite frustrating...

Thanks for any solutions you can suggest.

Jim