Files that cannot be opened by MAC are files with the extension “.pub” created by Microsoft Publisher.
If you are using Windows, it seems that you do layout etc. with this Publisher, but you can not open it with MAC, and it is quite troublesome if you get a “.pub” file.
I found a website that can convert such “.pub” files to PDF.
That is this site called ONLINE 2 PDF.COM !
Usage is simple.
Click the “Select files” button at the bottom center of the screen, select and upload the Publisher (.pub) file you want to convert to PDF.
Click the “Convert” button below it.
It will take some time, but it will convert it to PDF.
The conversion accuracy is also quite high.
It is a highly recommended site because you can browse Publisher files even on MAC!