[vengeance_2012]

Why:
I think JD2 is the only software who can use a password list to extract packed files that uses a password list.

Problem:
I downloaded some stuff and removed it from the download list without extracting. Now the rar files wants a password.... I know this password is saved in JD2.

Solution:
Extract the rar file with JD2 (plugin) or the JD2eXtractor software.

[Jiaz]

@vengeance_2012: not required, already possible out of the box.
JDownloader window-> Tools -> Extract files and there you can select archives on disk.
JDownloader will make use of password lists and its extraction settings for this.