Ive done part 1-4 and some of part 5. Ive come to the file named 'solution' but I cannot go any further. The answer is probably so easy Ill go kill myself after asking this by embarrasment but I cannot figure it out.

Ive now installed a program (WhatFormat) so I can scan it for the right extension but it only says .flt which is an extension Ive never encountered before.

.flt is not correct.

If you use some linux or unix system, they have nice utility named "file";
So if you don't know what type of file you're dealing with, just use this command.
Good luck

If you can't read it, try looking at it .

I dont have neither Unix nor Linux so that wont help me. I think I saw a previous thread where it was stated the filetype is pretty old. Is that correct?

Old or New it doesn't matter - google is your friend.

Eh, should I search for a solution? Isnt that cheating? Or do you simply mean to search for a list of filetypes?

There isn't really anything to google in this challenge, iirc...
Some programs will tell you what filetype it is or wich one it should be.