Not everyone can afford to hire an editor to proofread their documents for errors. Fortunately, there are a number of free software programs that can check your text for grammar, punctuation, word choice, wordiness, and other features.
Once again, the folks at The Write Life have provided a helpful review of six popular grammar checker tools: https://thewritelife.com/automatic-editing-tools/
These tools go beyond the basic flags (colored squiggly lines under words) you get from Microsoft Word. My favorite is Grammarly, which you can attach to Word so that it's always available to click on and off while working on a document. This allows you to edit as you write. The software also provides synonyms for words so you don't have to toggle back and forth between your text and an online thesaurus. Most useful are the explanations provided for why a grammatical correction is needed, so you can learn from your mistakes.