PDIFrame is a package which act as a plugin for the TinyMCE Editor within umbraco. It allows you to add an iframe to the editor with 1 click of a button.
After installing the package, you MUST change the umbracoSettings.config and set TidyEditorContent to False. Otherwise Tidy will still strip of your iframe upon saving of the document.
Before installing, make a backup of your tinyMceConfig.config because this package will overwrite the existing one.