The requirement of polishing is paraphrasing some sentences that you think would improve the document (at least one out of three sentences need to be paraphrased), then proofreading/improving the rest contents. So basically, polishing means heavy editing, you have to make a lot of changes and some paraphrasing to improve the overall quality of the document and improving the writing standard of whole document.
Quite confident in pulling this job off. I write research based articles, FAQ's and similar documents. I am a final year uni student with strong skills in technical writing.