Opening a PDF with Adobe Reader DC prompts to download a font package, but does not. The document then fails to display portions or the entirety of the document.
1. Navigate here to find the Font Pack from Adobe: 32-bit Font Pack and Spelling Dictionary Pack for Acrobat Reader DC on Windows (adobe.com)
2. Download the Font pack version that applies to you -- most commonly will be the latest version. Currently that is 2021.x (Continuous).
3. Close out of any running instances of Adobe Reader, and then install the downloaded package. You may need to close other programs that utilize Adobe Reader as well.
4. Once done, open the document again -- It should display correctly now.