Can't create a Database on Oracle 11g
In a command line, run:

attrib C:\Users\Pierpaolo\Documents


If you see a capital R in the output, then the read-only attribute is set for that folder (which is the default setting for the Documents folder).

Either remove the read-only attribute from the folder (I do not know what this will mess up in Windows), or specify a different folder for diagnostic dest.
For the latter, on this screen, go to All Initialization Parameters..., and set the value of diagnostic_dest to a directory that has no read-only attribute set.