MediaObject may be used to describe e.g. PDFs (see https://lists.w3.org/Archives/Public/public-schemaorg/2016Feb/0027.html), not necessarily embedded on a page. Here is a proposal to broaden the definition accordingly :

Current :
"An image, video, or audio object embedded in a web page. Note that a creative work may have many media objects associated with it on the same web page. For example, a page about a single song (MusicRecording) may have a music video (VideoObject), and a high and low bandwidth audio stream (2 AudioObject's)."

Proposed :
"An image, video, audio, or other kind of media embedded in or linked from a web page. Note that a creative work may have many media objects associated with it on the same web page. For example, a page about a single song (MusicRecording) may have a music video (VideoObject), and a high and low bandwidth audio stream (2 AudioObject's)."