The correct password is required before WinZip® can extract an encrypted file from an archive. If WinZip does not already know the correct password from a previous operation during the same session on the same archive, it will ask you for the password when it is needed.
Note that WinZip extracts files not only for the Extract operation, but also when you view or open a file and when you use features such as Test, CheckOut, Install, and Virus Scan.
You can encrypt files while they are being added, or you can encrypt (or re-encrypt) all files already in a Zip file.
Encrypting files while adding
The most efficient way to encrypt files is to do so while you are adding them to an archive. To encrypt files while they are being added, simply check the Encrypt added files check box in the Add dialog. Before adding the files, WinZip will display the Encrypt dialog, where you will specify the password and encryption method.
When you add files to a Zip file from Windows Explorer, you will have an option to encrypt the files if the Add dialog is displayed. In some cases, however (e.g., when you choose Add to recently used Zip file), there is no Add dialog and therefore no opportunity to encrypt the files while they are being added. In these cases, you can encrypt files after they have been added, as described in the next section.
Encrypting files already in a Zip file
To encrypt files already in a Zip file, either
If a file in the Zip file is already encrypted, it will first be decrypted and then re-encrypted using the method and password you specified. WinZip will first try to decrypt the file using the current encryption password; if the file cannot be decrypted with this password, WinZip will ask you for the correct decryption password. If you are unable to supply the correct password, the file will be skipped, and it will remain unchanged in the Zip file.
Note that it is more efficient to encrypt files while they are being added to the Zip file than to encrypt them after they are already in the Zip file.