I don't think you will get much help for DRM removal on the Digital Edition forum.
You won't be able to make any changes using ADE prior to DRM removal.
After DRM removal you will have a standard .epub or .pdf.
There are several DRM removal tools, I don't know how similar the result are: try EPUBEE.
For a .epub you can massage details such as fonts in Calibre.
If you are more technical, you can open the .epub using a zip manager such as 7-zip and see all the files.
You can then edit the .css files, and any font files that may be embedded, or even the individual .html files if easier.
...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...
Could still be a DRM removal problem.
Given what you say, the first thing to do when you unzip the stripped .epub is to look at one of the .html files.
It should be easily readable text (in so far as HTML is ever readable).
If not, something has gone wrong in the DRM removal.
For comparison, you can use 7zip or similar on an original DRM .epub, and on a successfully stripped .epub, and look at the .html files.
I have found a small number of library books .epub that opened fine on ADE, but would not open on a Bookeen Opus.
I never found out why, and wasn't that motivated to try to read those particular books.
It may be that there are slightly different ways the DRM is applied, and that some can break both strippers and some ebook readers?
Still may be worth trying another stripper.