Scanned PDF won't open in Reader w/o "font package"

Recently scanned documents as PDF with my Epson WF-7620. No issues creating or saving them. Used the latest firmware and drivers. Was able to view them on my Windows PC at home. I emailed the documents to a third party and they were unable to open them. I confirmed on my work computer that I was also unable to open them With Adobe Acrobat Reader DC (version 2015.008.20082)on my Windows PC and got the following message:

"A font package is required to correctly display this page. Click "OK" to direct your browser to download the add-on from adobe.com. After installation, you will need to close and re-open the document to correctly view the contents dependent on these newly installed fonts."

Due to security restrictions I'm unable to download or install whatever font is necessary. And I don't understand why a specific font would be needed. It's a PDF, there were no unusual characters or languages in the document.

I reviewed the various similar questions in the forum and saw no clear answer as to how or why this problem is occurring or how to guide the person that I've sent these important documents to as to how to open/view them.

Also, I WAS able to open and view the documents in Adobe XI Standard without difficulty. So why is the Reader unable to open this and how should I guide the party trying to view this?