Hi there! Pit bull owner here. Unfortunately, I'm not a drug dealer, gang member, or antisocial thug... unfortunately for you, anyway, because otherwise this description of my job might be a little more interesting!
No, the cold, hard truth is that I
heart love grammar.
My experience is with textbooks, specifically middle school and high school literature textbooks. But I've also been on a copyediting team for a technology RFP (a work proposal for the state), and I've done a bit of history, social studies, and psychology textbook copyediting as well.
Sometimes I work on hard copy (paper) and sometimes I work on PDFs or Word documents. It just depends on the job.
This stack of paper below is a grade 9 test handbook; it is what teachers use to give tests at the end of each unit in the textbook. It also has an answer key and a skills chart (that the teacher can review to see what state skills the students are learning).
I usually work on my dining table, or on the living room couch. Byrd built me a huge desk where I can spread the papers out, but then he took over half of it!
Here are the supplies I use to copyedit: a mechanical pencil (or a colored pen), an eraser, a ton of small sticky notes, some "sticky finger" wax, and page flags. The page flags are cut from the small sticky notes.
Here's the copyediting in high gear. I've split up the pages so I can check cross references--that is, references to other pages in the book. I also have to check the answer key and the skills chart for each question.

I'm checking for grammatical errors, typos, incorrect answers, style inconsistencies, and pretty much anything that doesn't work or make sense. I mark and correct most of the little issues directly on the page. I put queries--questions for the editors, usually about issues I can't resolve because they are too big for a quick fix--on sticky notes on the page.
Any page with any sort of mark or query must have a page flag, so the editor knows the page has been "touched."
This particular document was supposed to be "mostly clean"--that is, it wasn't supposed to have a whole lot of problems. But you can see from the page flags that "clean" is a subjective term!
Here are some other important supplies: a big bag of pecans and a tray of cinnamon rolls. Other staples include Coke, Oreos, chips or popcorn, apples, cheese and crackers, and anything else I can stuff in my mouth with one hand while writing and turning pages with the other.
Of course, it's important to have a laptop or computer on hand. Not only do I use an online dictionary/thesaurus, the online Chicago Manual of Style, and research sources for fact checking, I also listen to J-pop (Japanese pop music) on Web radio while I work.

Why J-pop, you ask? Aside from the fact that I like it ("NERD!"), it's also very difficult for me to sing along. When you're trying to read and edit a document in English, the last thing you want to do is listen to music in English. Pretty soon, you're so busy rocking out to the lyrics that you've lost concentration (and probably missed a bunch of grammatical errors). With J-pop, I get a nice tune that keeps me awake without confounding my language skills.
And yes, I've tried classical music, which has no lyrics at all. It puts me to sleep!
So, there you have it. After I'm done with the entire document, I turn it all in and wait for the next job.
If you're thinking this is sort of an unusual occupation for a pit bull owner, let me break it to you gently. You should know that most of us actually do have normal, boring jobs as teachers, writers, technology experts, doctors, and so on.
Sorry to disappoint.