How can I compare two Google Docs documents within an Appian application?

In my opinion you will have to download a local copy of those docs in Appian. Then work with plugin Apryse WebViewer Component Plug-in . It features document comparison in semantic categories. Compiling the output from the plugin execution you can then show them in Appian. 

Apart from plugin, You can build AI Skill as well to compare contents of the documents and get the differences. But as AI can make misses, a review will be better. So you can try working with AI skill as well depending on how structured the docs are. 

In my opinion you will have to download a local copy of those docs in Appian. Then work with plugin Apryse WebViewer Component Plug-in . It features document comparison in semantic categories. Compiling the output from the plugin execution you can then show them in Appian. 

Apart from plugin, You can build AI Skill as well to compare contents of the documents and get the differences. But as AI can make misses, a review will be better. So you can try working with AI skill as well depending on how structured the docs are.