If you're annoyed with
Fill & Sign /
Comment right sidebar in Adobe Acrobat Reader (it is pretty useless, but still occupies a lot of space), then you can hide it with a simple trick.
Press Ctrl+H or select
View > Reader Mode to enable Reader Mode.
This will hide all extra stuff (all toolbars and sidebars) except actual document area. If you would like to bring left sidebar (with navigation panel etc.) back, then simply press that keyboard shortcut or select that menu option again, to disable Reader Mode. Left sidebar should return, while right sidebar should remain hidden.