Citing paywalled articles accessed via illegal web sharing There are a few sites which offer paid articles for free. It’s something unethical, especially for those who upload to that site, but for me, it’s good for expanding knowledge.

As a readers, can we cite those documents, and can the editorial board know that I’m using those articles?
Nobody will know how you have gained access to the article. Feel free to cite articles found via whatever sources.
It might not even be illegal to download content from the website; check your local laws and Berne convention (if your country is signed up) to be sure. In any case, this is unlikely to affect your reputation in any way.
Remember to cite the source appropriately; a journal or a book, not a pirate website or any other medium. The pirate website is usually not the publisher. You do not cite the university that has bought access to research (probably funded by public sources and peer reviewed by academicians funded by public sources), or the colleguage who shows you an article, or the library that contained a copy of the article; these all have the same role as pirate website.
You might not want to be vocal about using such a website. Some people still see it as ethically questionable. That said, using various pirate websites is increasingly common, and the status of many academic publishers among academians seems to have taken some hits, so many researchers will not care about how you get your articles.
You also have the ethics tag on the question. The ethics of pirating digital material are a polarized subject. You might want to do your own research here, or ask a new question for what the main arguments for both sides are, if it has not been asked already. Some people say that pirating material is analogous to physical theft, while others say that intellectual monopoly laws are bad and breaking them creates more good than ill. (I happen to think the laws are far too strong and harm humanity, and should be weakened substantially or entirely removed.) I strongly suggest reading on the matter until you have found strong statements of both points of view to come to an informed decision.