I would like to report a significant issue that has arisen with the latest update, particularly affecting the display and functionality of PDF Portfolios. Formerly, these portfolios showcased thumbnails that provided a visual preview of the contents, enhancing navigation and user experience. However, these thumbnails are now missing, replaced by a mere list format that significantly diminishes the portfolio's usability and aesthetic appeal.

Upon switching to the old UI, hoping to regain the lost functionality, I observed that while the thumbnail pane reappears on the left side, it only displays PDF icons instead of the actual thumbnails. This change not only impacts the visual representation but also the ease of navigation within the portfolio.

Moreover, the new "list" GUI introduces a cumbersome process where files are opened in separate tabs, disrupting the seamless browsing experience previously facilitated within a single tab in the old GUI. This crucial feature's absence cannot be overstated, as it significantly cripples our ability to navigate through files efficiently.

Navigating clients through the process of downloading Acrobat, setting up all the necessary preferences, and then instructing them to switch to an older interface — only to discover that even this UI's functionality has been diminished, as thumbnails within PDF Portfolios no longer display correctly — is embarrassingly awkward. It places us in the uncomfortable position of having to apologize for inconveniences that should never have occurred, all the while questioning what further complications future updates might introduce.

It's crucial to remember, Adobe, that as we bring new customers to your platform, the usability challenges imposed by these updates not only affect our workflow but also complicate our relationships with those clients. This time, the changes have made it significantly more difficult to advocate for your software.