Go to Documents.
Point to the document you want to set as a favorite and select the star icon. (Or, on the More Options menu, select Star.)
Documents that are favorites are shown with the star icon.
Remove from favorites
To remove a file or folder from your favorites, simply unselect the item's star. Alternatively you can also manage this from the three dots menu.
View your favorites
To view your favorites, click the filter icon in the search bar. Then select the Favorites quick filter.
To remove the filter, simply unselect Favorites in the filter dropdown, or click Clear all.