Version 20.01.00 for iOS allows you to open an html e-mail attachment much like it is possible to open a .pdf. This no longer works in 20.02.00. In version 20.01.00:
1. You could open an html file attachment, tap on the share icon in the upper right corner of the screen, and then choose the Adobe icon to import and open the html file.
2. Optionally, you could do a long press on the file attachment, choose share, and then choose the Adobe icon or "import to Acrobat."