PDF created on PC in Adobe Acrobat 2017 cannot be opened on iPad and iPhone

I didn't have that information when I posted this; however, I sent a document to my own iphone just now, and it open with no problem. My boss sent a different document to both himself and to me, and neither of us was able to open it. The PDF downloaded, asked for the password. But it just kept going back and asking for the password again, and again. The PDF will not open on our iPhones. My boss was able to open it on his iPad. Since some of our board members were able to open the document, and some were not, I wonder if this has to do with a setting for the devices.