Hi sjpt...
...thanks a lot for your help! I'm not having problem with the DRM removal itself...all the e-books that I've purchased I've already converted with Calibre to .mobi and sent to my Kindle...just that one - I can't deal with it...That's why, I think that the problem is with the font of the original (DRM protected) e-book...when I open it with ADE, I can read it, but when I add it to Calibre - there are just symbols (aaaeieieieooiaoioe...etc)...before even to convert it to .mobi...
I'll try what you've advised with the 7-zip and hope that it'll work...thank you once again...