As a Joomla developer, you encounter many things that are not easily answered, like "why can not I get this iFrame to work on my site?" Or your client requests "how difficult will it be to place a page from one of my other sites within the Joomla site you are building for me?"
Being a seasoned professional as well as a resourceful person you of course will tell your client "That's easy enough, I'll get right on it." Then comes the mad dash to figure out how to make your client happy. Well, it's really not that difficult to embed an iFrame, and I will walk you through the steps, but first there are a few assignments I have made about your skills set. The first is that you understand and know how to access the administrator area of your Joomla site. The second is that you understand what iFrames are and how they work.
The most likely cause of your accessibility to embed an iFrame in to your site is that you are coming up against a "blacklist" in Joomla. All versions of Joomla since version 1.5.8 have had a "blacklist" function that protects the site from accepting actions that can cause possible security problems. These actions can prevent embedded files from being posted without proper permissions. The first step in preventing iFrames is to set the site permissions so that you, as the Super Administrator, can embed files and protect your site from others who want to embed files.
To do this, go to the "Content Menu" and choose "Article Manager", then click on "Parameters" in the upper right corner. A new window will popup, you will want to scroll down to "Filtering Options". Select all choices except "SuperAdministrator", next hit save and close the window. The steps you have just completed will enable anyone logged in as a super administrator to embed ANY code in to the site. These actions also will prevent anyone else from embedding potentially malicious code with tags such as embed, body, and head. Please be advised that only articles created after you make these changes will be allowed to have code embedded in to them.
If your articles continue to not accept the embed code, it may be due to using Tiny MCE, a page editor program that appears as a bar of editing tools at the top of your article body text box. Tiny MCE runs its own security against joints due to embedding code and you will need to shut Tiny MCE off before you can embed anything.
To turn off Tiny MCE, go to the "Site Menu" and then "User Manager" and select "SuperAdministrator", which most likely is only you. On the right, under "Parameters", change the "User Editor" from "Tiny MCE" to "Editor – No Editor" and click Save. Next, you will want to return to the article you were working on, confirm there are no editor tools at the top of your body text box. If the tools are no longer there, you should now be able to paste the iFrame code into the article body text box with no problem.