The text editor used for Authoring KA content has introduced a feature that automatically adds a 'sandbox=""' tag attribute to any iframes added to the HTML content of an answer. This will typically result in errors when PDF content is used in iframes. This attribute was introduced to avoid security vulnerabilities, and the behavior is considered appropriate and working as designed.

If needed to get around this feature, before saving the document, the author can toggle to Source Mode and Save it (after removing the 'sandbox=""' attribute) without toggling off the Source Mode. This has to be repeated every time Author performs a Save, and the correct syntax can be confirmed by viewing the HTML source (right-click View source in Windows) in the answer view after saving.

This can be confusing, because if the HTML editor is opened back up, you will find the sandbox="" text there again. Also, if you edit a small change to some text (not the HTML, and not the HTML view) in the editor - and then save and view the source again - you will see the attribute there again (and will need to be removed before the next save).