If you have a .txt file with multiple accounts (from some dubious "database"), JD2 does have a bulk import button by default. However, you can use the Account Clipboard Monitor :
Third-party “premium databases” or “leaked premium accounts” almost always: jdownloader 2 premium database premium account install
Always ensure you are using trusted sources for database files to protect your privacy and system security. How to Install a Premium Account in JDownloader 2 If you have a