Download Issues with iOS (iPad, iPod, iPhone)
iOS devices like the iPad, iPhone, and iPod are fundamentally unable to download and store files from the web. They will try very hard to display them, however. As an example, PDFs will display in Safari just fine, but you can't save them from there, you can only view them.
For other types of files it will try to open the proper application to view those files. If it can't find one it will ask what application should be used. See screenshot below:
If you or your customer need the file on your iOS device we recommend it be downloaded on a computer first, and then use iTunes to transfer the file to the device. Instruct your customers to open the email receipt from their main computer, and transfer the file to their device using iTunes.