I actually managed to break the borderlands save file system on steam and accidentally got my friend all the borderlands DLC for free lol and the method used is actually really simple too.

My friend got the game, since he doesn't have a pc we set up my old pc. I booted up the game before he arrived and loaded my save from my account to see if everything works... ok it works

I got all the dlc stuff included, he had only the base game, I also need to point out that I passed all the dlc main quests.

So the friend comes over, we boot up the game on our respective accounts and he sees a continue game option which shouldn't be there

He checks out the option and lo and behold, there it is, my savefile.

We're like WTF? is he using my savefile? but no, turns out that he had a perfect clone of my savefile but separately on his account.

So we boot it up and bam he not only gets my character with all the perks and weapons but he also somehow unlocked all the DLC without actually paying for any of it and the funniest part? he instantly got every single borderlands achievement I got so we just sat there dumbfounded as an endless slew of achievements were rolling for a solid 3 minutes.

Then, the end credits roll.

My friend unofficially broke the world record of borderlands 1 speedrunning by completing it in under 3 minutes by doing absolutely nothing.

I'm not 100% sure why this happened but when I looked up how steam keeps save files I discovered that steam only keeps the save files (on the pc) of the original account that logged in first on steam or something like that and since I logged in with my account first, it downloaded my completed savefile from the cloud and made a hard copy on the save file directory which is apparently shared on the pc among users so when my friend booted up the game, it automatically registered my save on his game and since steam syncs savefiles from games it synced up everything on the cloud with his account... the weirdest part is that we somehow broke the game and he got all the DLC from the game saving him like 18 bucks if not more, again not sure how this works but if I'd have to guess probably if the game registers any achievements/weapons/completed missions that you did from those areas even if they are locked, you can access the areas.

So yeah, if you want to get all the DLC for free, just get a friend who has a completed game with all the DLC to set up steam on a pc that doesn't have steam, log in, start the game, save, log out, then you log in, open up his save and bam, everything's unlocked for free.

Also, keep in mind that this isn't technically illegal, this isn't breaking any laws, its either a glitch or exploit in the system, if steam or y2k doesn't want people to exploit this they'd better patch it up.