In general a copier will handle small jobbs without collating/stapling/editing of color and so on in RAM. Other jobs are stored on disk. But the next job will overwrite the last job more or less.
Only documents stored with purpose on the drive (doc centers functions) will be saved in a way that is fairly easy to gain access to (even though you need special software to do so). Even if you store in PDF, it is usually not a standard format that is stored to the disk (minor charges is made to the format). We tested this at work.
Oh yeah.. also if people store jobs on the machine and get the pages when they type a code.. those jobs are also stored on the drive. We managed to get several pages from that area too.

All new copiers have security features like data overwrite security units and they usually also have the ability to encrypt the documentes. All this will take some extra seconds. Nothing that the average user will notice if they had it that way from the start - but if you add the feature they might notice once in a while.

A few years ago a friend and I went to electronics recycling area - where PCs were stored for a few days/weeks before it was sent to the recycling facility. We harvested a few machines and extra drives and RAM. It was amazing. Not ONE single PC had the content removed. We got personal pictures, hospital records and grades from a school and so on.

At the same place there were mountains for paper that was stored before recycled. It was several hackers/crackers that were dumpster diving for passwords or just info to get names and how a company was structured so they could use social engineering/hacking to get the info they wanter. Like.. hi Jane, this is John from IT. Peter told me that the PCs in your department was a bit slov. We're going to try to fix that. Can you give me your username and password as I'll try to sort it out. Oh by the way, you're getting a new laptop in December. Do you want it in silver or champagne color? I see wendy at accounting wanted champage because it was SOO stylish.. and so on. In a few seconds she will give them all the info they want.

So a good rule it to wipe all drives weather they are in a PC, TV or a MFC. Use a serious tech company to maintain your equipment that will do it for you. Shred ALL documents, no matter if they are secret or nor. It will make is so much harder for folks to get info from a pile of paper then from just a small plastic bag full of secret documents.