If you protect a collection with a password then you can designate clips as being secret. AceText does not show the contents of secret clips unless you click the Reveal button. The secret is hidden automatically after a configurable number of seconds, unless you’re busy editing the secret. When you use 
AcePaste to transfer a secret to another application, AceText always does so by simulating keyboard shortcuts. AceText does not transfer secrets via the clipboard as that would make it all too easy for other applications to snoop on your secrets or even for them to be accidentally pasted more than once.
If you have other applications like password managers that do place sensitive data on the clipboard, you can configure those so that AceText won’t automatically show or capture their data on the Clipboard or ClipHistory tabs. If you then manually paste data from such an application into a password-protected collection then AceText automatically treats the new clip as a secret.
Or you could use AceText itself as your password manager. The 
Generate Random Clip lets you generate new secrets with random characters strings that must or mustn’t contain certain characters, as is often required of passwords. When a collection is protected with a password, AceText uses a slow algorithm (PBKDF2) to derive a 384-bit encryption key to make guessing the password infeasible. It then uses a hereto unbroken encryption algorithm (blowfish) to encrypt the collection. Without the password, the contents of the collection cannot be recovered.