I just took over a WP Website and the Google Doc Embedder Plugin wasn't working. I found two inconsistencies and changed both, I'm not sure which one fixed the problem but its working now.
1. The default plugin height and width settings were different from the settings specified in the code snippet (I removed the settings from the snippet):
[gview file="http://full-path.to/file.pdf" height="400" width="400"]
2. Changed the default setting in the plugin from "Enhanced" to "Standard"
Use this option to improve IE compatibility and enable toolbar customization.
Google Standard Viewer
Use this option if you experience problems with the Enhanced Viewer.