Will someone know if you save their voicemail to your own files on iPhone?

They won't know if I do this right? I wanna save a voicemail to my files but I don't want the person who left the voicemail to know.

Look at it this way - when you call someone and leave a voicemail, do you then get any notifications afterwards?

Do you get a message which says "John Smith listened to your voicemail"

Nope. You don't. The person who leaves the voicemail has no way of knowing what you do with that voicemail. They don't even know whether you heard it, unless you say something to them.

So if you want to create an audio file from a voice message and save it on your phone, no one will know.

Unless you tell them.