You can check grammar and style suggestions using the Check Grammar of Selection. This feature works by showing Grammar suggestions in a Diff Window that shows original and fixed text side by side along with an editable block of the fixed text below:

You can make changes to the text below which updates the Checked display on the right.

You can click the Accept button to apply the changes against the active selection of the original text in the editor.

Keep Selections small

This feature tends to be somewhat slow to process especially on larger blocks of text so we suggest you keep this to one or several paragraphs at a time.

It's also easier to work with smaller checks rather than the entire document both in terms of performance as well as being able to see the and manage the changes.