When downloading files using JDownloader, some files especially those that are compressed and password protected will fail to extract upon completion of the download and ask for manually entry of the same. This happens because by default, the password for these files is not stored by JDownloader.
In order to store passwords for files being downloaded so that downloaded files are automatically uncompressed or extracted without manually entering password for doing that :
Open JDownloader and go to Settings.
Then select the “Password & Logins” tab  and then click on Unrar/Extract. This will list all the possible passwords that will come in use on the right. This happens when you download various files from different sources and each package as a whole needs a password for it to uncompress, all of these passwords can be saved one by one as a list in the right pane.
This is a useful feature of storing the password list and is time saving when using specific download sources which have the same few passwords that are needed to extract the downloaded files. JDownloader looks through this password list every time it encounters a password protected file that needs to be extracted, so it’s best to keep regularly used passwords here for automatic extraction.
Happy downloading.