This is the collection of Project Euler problems repackaged as pdf's and in other formats, so you can download them all at once and work on them offline.
I clicked the link thinking it meant something different, that Project Euler's website (projecteuler.net) itself was down. But it is working fine, at least at the moment. You can all relax.
Offline assuming you know enough theoretical math to be aware of the trick you inevitably have to know to get the solution without a search engine, I suppose.
Project Euler was a cool idea, but it always feels to me like the worst of Leetcode interviews and the worst of riddle interviews combined - it's not that your solution will be suboptimal, it's that you will not be able to solve many of the problems before the heat death of the universe unless you know this one weird trick.
This is the fun and annoying part of the PE problem set :-) I work on them purely for fun, and suddenly with years between. Some can definitely be a bit annoying, but their purity and conciseness makes it possible to store problems in your head and keep thinking about them for a while. I've never felt cheated by the problems, as often there will be several ways to solve something, and it feels really fun to shave down the running time by improving an algorithm. They are also very well stated, so there's rarely any mistake or edge case issue with them (my experience is in the first few hundred).
Some problems are just fun to work out mostly through code, like Poker Hands [1] or Monopoly [2], and other more geometric ones like Magic 5-gon ring [3] or Hexagonal tile differences [4] are nice to just reason about on paper. These don't really require much specific knowledge. For problems requiring more knowledge to find useful tricks to solve the problem, I'll often load some related Wikipedia pages I can study on a flight or train ride.
It's not really about knowing the one weird trick. It's about FIGURING OUT the one weird trick. Yeah asking anyone to do any but the easiest ones in a realtime format would be sadistic. They are math problems and you are supposed to think about them, in some cases for quite some time. They aren't coding exercises, though you can use the early ones that way.
I clicked the link thinking it meant something different, that Project Euler's website (projecteuler.net) itself was down. But it is working fine, at least at the moment. You can all relax.