Is it already on your roadmap for your product to be upgraded from flash before salesforce discontinues supporting flash products in Dec 2020?
@NYoung and @himes - We have available now a new Lightning Experience DocGen Package Designer (LEDD) for managing your docgen packages in Salesforce Lightning that removes the dependency for Flash. You can find more details here:
The new Designer is currently still in Beta, expected to be GA released around April 2020 when we plan to wrap up support for all document template options when configuring a DocGen Package.
@himes - We are shifting all new feature development for DocGen Package management now to focus on the Lightning experience within LEDD. Once Salesforce (Oct '20) and browsers (Chrome in Dec '20) stop supporting Flash, you will be required to us Lighting to manage your templates. Other features that do not use Flash, such as Delivery Options, you can still manage in Classic.