@suzanne_2106 technically you can open your 2017 Acrobat, using it for any kind of productive, secure, and integrated collaboration within your company's Teams GCC-High environment is likely impossible and, more importantly, a significant security risk. The system itself is probably blocking it because it doesn't meet the necessary compliance and integration standards for that highly secure cloud. Adobe officially ended support for Acrobat 2017 Classic and Acrobat Reader 2017 Classic on June 6, 2022. This is a major factor.
the paramount reason is your GCC-High environments have extremely strict requirements. Your 2017 perpetual license, being unsupported and not designed for deep cloud integration, simply doesn't meet the rigorous security and compliance standards necessary for file sharing, real-time editing, and collaborative workflows within that highly controlled Microsoft cloud. The system is designed to prevent unapproved or insecure applications from interacting with sensitive government data.