Yes, you can combine more than one document and copy/paste in Grammar Check. As Grammar Check examines each sentence individually and notes if there are any grammatical mistakes in it. It does not check if there is one or more document that has been submitted for checking. Its routine is to check each sentence and if it finds a grammar mistake it points it out. Therefore you can copy/paste two or more unrelated documents and it will check them based on its own algorithm. This facility has been provided as students might want to check a geography assignment along with an economics assignment. Grammar Check works sentence wise and there can be just 5 or 500 sentences. It will evaluate each sentence independently. However we suggest that you avoid this practice. The reason for this is that submitting more than one document might lead to confusion, not for the Grammar Check application but for the user.