Hello @UCMGCC16 ,
I was able to test send your last email to myself, and open every PDF in it without issue. I'm wondering if your mobile device isn't fully updated or is lacking what's needed to read PDF files. It's also possible that the browser you have set as your device's default isn't fully up-to-date or allowing the PDFs to load. Since PDFs are hosted in your Library on our system, it will most likely have to do with the settings for your device's browser.
It may also be worth seeing what your device uses to read fully downloaded PDFs normally, and see if that app / function is fully updated. Otherwise you may also wish to reach out to your applicable device's support to see if they have any insight on why the PDFs won't load.