Document editing is a layered process . At the topmost layer is contextual editing, which is best performed by a human editor. The basic layer of grammar corrections can be performed by digital tools.
While most word processors such as MS-Word and Apple Pages have built in grammar checks, there are also other free online software and apps that can help with grammar checks.
At Valardocs, we use Grammarly for the first level of grammar check. Our copy editors use this tool to correct obvious errors in the document before they delve into contextual editing, which is our forte. Grammarly also has a rudimentary plagiarism check built into it, and this can be of great help to academicians. There is a free version of grammarly that performs basic grammar checks, and a paid version that does more. We use the free version and for the "more", we only trust the human brain.
There are other free sites that can help you with grammar checks. Some of them are:
Until then, you have us.