Thanks for four quick reply! I attached 3 files, which DoubleCAD XT didn't open.
The first one is huge, it's an architectural plan of a Burger King, I got it from a procurer and I don't know what software was used for drawing it. I edited it in AutoCAD 2009 and it gave a message when opening: it wasn't made with Autodesk software. Anyway ACAD opened it correctly, DCAD didn't.
The second is a small kitchen floorplan I made for a friend with ACAD 2009.
The third one was also drawn completely in ACAD 2009.
They contain no solids or surfaces, but everything else (dimensions, hatches, annotations, texts, some blocks...)
DCAD crashes when I try to open the first and the second and it gives an error message for the third.
If needed I can post some more.
Hope this will help!