I found the solution!!!!!!
That's a setting in sh404 config>plugins>docman
If you want to include a "root" word in your docman URL, you have to tick the box (first parameter)
THEN go to sh404 config>plugins>per component
in the last column, write the word you need in your url!
I had problems with Xmap and the module ultimate download for docman, the links were completly fucked but now it's fully working