The movie came out in '99, was written a year or 2 earlier, the frustrations of MS DOS were still pretty recent.
In a well-run company the manual for a shared printer ought to be kept with the printer; at Initech, Milton probably has the manual in his desk, under an apple core.
What you’re forgetting is that all printers are useless pieces of trash that never work right.
I had an old HP LaserJet 4M printer in my office years ago. As a Computer Science prof I used the “PC Load Letter” message in my classes as a prime example of unhelpful error message. Years before Office Space.
I still have a (different) working LaserJet 4M as my backup/heavy duty printer. Toner cartridges are cheap now and you can print a ton on one cartridge. But sloooow.
Those things last, as long as you don’t take a baseball bat to them. OTOH, they don’t have enough flair.
Not as easy as it could be. Manuals are notorious for NOT providing alphabetic lists of error messages with an explanation for each.
This is compounded by programs or devices with software written in some intermediate language or template. Even a comprehensive list of common errors like “paper jam” or “out of paper” would omit compiler errors (“undef var line 398”) on the theory that they never happen. But they do.
I have several sophisticated video cameras, and sometimes a symbol pops up on the screen that I don’t recognize. (Typically, I bumped a switch by accident.) It’s difficult or impossible to diagnose the situation because there’s no master symbol list, and even if there were, how do you alphabetize icons?
‘PC Load Letter’ was meant to alert that paper was needed in the tray, but it displayed every time the crappy printer thought it needed paper in the tray. Paper jam, misaligned tray, wonky roller, toner dust, out of gas, flat tire, change for cab fare, tux at the cleaners, locked keys in the car, old friend came in from out of town, car stolen, earthquake, terrible flood, locusts…PC LOAD LETTER!
My old job had a printer with “PC Load Letter”. I quickly noodled out what it wanted (just by opening trays and the top, etc to see what looked wrong) but couldn’t have told you what “PC Load Letter” was supposed to actually mean.
Backups? Most likely. Off-site backups? They should, but it seems like the sort of expense that someone might deem unnecessary.
I know from personal experience that 9 times out of 10 the people who write the manuals are the same engineers who wrote the software, so good luck thinking the manual is any clearer.
Similarly, I think the people who design the equipment rarely use the final product.
See Eating your own dog food - Wikipedia
“Eating your own dog food, also called dogfooding, occurs when an organization uses its own product.”
I like it. Certainly more realistic. 
If they did make the error message “Out of paper”, then some clueless user would try to jam A4 paper into the tray when they were trying to print something proportioned for US letter paper, and what does the printer say then? “Wrong paper”? Then the user will try colored A4, or A4 of a different thickness, or something. You have to tell the user what kind of paper they need to load, and the kind of paper they need to load is US letter (of any color or thickness).
They had the minimum amount of flair required, so what’s the problem?
Just released last week:
Last year our local Alamo Drafthouse showed Office Space as a movie party, including their usual little toy props and an actual printer-bash. They put an old laser printer on the floor between the screen and row 1, gave a few volunteers a bat and actually played the signature rap song while they smashed the thing to smithereens. The toner cartridge actually exploded in a black cloud when they broke it. It left a HUGE mess. But that was a fun event.
My company once had a group of IT workers housed in a temporary workspace (read: trailer). This was in the relatively early days of PCs, and everybody backed up their own computers on floppy disks. And where did they keep the floppies? Typically, right next to their monitor. Well, some kind of critter (rat, IIRC) got into the roof, built a nest, chewed some wires and caused a fire.
The trailer was a complete wreck, and all those backups were melted along with everything else.
The bits (Im paraphrasing) about “Yeahhh yeahh. Oh yeahhh thats what I want. Yes PLEASE KEEP DOING THAT.” With the copier is some of the best acting Ive seen.
/nitpick “Mr. Gittes”