Recently we changed the embed behavior for petition pages. By default, videos and images will embed normally, but pdfs will no longer embed into a petition.
However, if you still want pdfs – or other non-video/image media – to be embedded into the petition page, you can force this behavior by appending ?showEmbed=true to the end of the URL. For example, http://files.neworganizing.com/toolbox/Strategy%20and%20Theory%20of%20Change/Presentation-online-strategy-toolbox.pdf?showEmbed=true.
Alternatively, if you don't want an image or video to embed, you can append ?showEmbed=false. This will display the link alone, not the associated media.