Creating an Apple Encrypted Archive with Archive utility: Why can't I choose a password?

I have never attempted to use the Archive Utility to directly archive or zip documents until now. I'm looking for something fairly secure for sending financial records and tax documents. I will be emailing these documents.

Using Apple's "Archive Utility.app" found in "/System/Library/CoreServices/Applications/" I changed the format in settings to "Apple Encrypted Archive" (file extension: ".aea") then I attempted to Create an Archive. It offered a password: example: "46230-41943-88756-67123-90710-43807" You can only encrypt using the suggested password, I assume they want you to copy and paste this somewhere or write it down so you don't forget it. I have never seen any encryption software that doesn't allow the user to use his own password.

Could anyone shed any light on this behavior. Also could someone recommend a common but secure encryption method for folders or single files. My mac can open password protected "Zip" files as I assume most Windows machines can, but is it secure and what app should I use to encrypt.