Working with Encrypted Archive
You can open encrypted archive in panel (see Archiver section in Using Plugins). You will be prompted for archive password or key. When you enter this password or key, the archive is decrypted (unlocked) and you can do all common operations in it (open, view, edit, copy, move, and delete files, etc.).
Security Issues
The View, Edit, and Open commands unpack focused file from archive to temporary directory. The associated viewer, editor, or other application works with this temporary copy of file from archive. When you close it, the temporary copy is deleted. This is a security problem because anyone can simply undelete this copy from the temporary directory. To avoid this problem, the plugin can shred (irreversibly delete) this copy.
Another security problem is that editors (and sometimes also viewers) create some auxiliary files beside this copy. E.g. when editor saves a new version of your file, it first creates a new file with a temporary name, then deletes the original file (or renames it to some BAK version), and finally renames that temporary file to original file name. Such auxiliary files cannot be shredded by the plugin because it does not even know about them. To bypass this problem, the plugin allows you to change temporary directory for temporary copies of files from encrypted archives to some suitable place. E.g. your USB stick (you can keep it on some secure place), or some small FAT partition which can be periodically shredded, see Cleaning Disk Free Space. NTFS partitions are not suitable for this directory because they have problem with shredding small files (smaller than around 1024 bytes), see Show warning "Shredding problem with small files on NTFS" on the Shredding tab in the Configuration dialog for details.
See the Temporary Files tab in the Configuration dialog for details on how to configure the plugin in this respect.