Being an IELTS and PTE instructor, I constantly edit and proofread essays. I use MS Word, with tracked changes and comments. Basically, my work involves: correction of spelling, grammar, syntax, punctuation, general improvements to overall flow and consistency, restructuring of sentences for greater clarity, language substitutions to avoid repetition, or to achieve a particular tone/style, and rewriting of broken or non-native English text to read as fluent.