Sometimes mobile devices will cause problems:
- Image quality is low - PDF appears pixellated and unreadable, or
- Toolbar is difficult to locate - it keeps moving out of view
These can be caused be conflicts within your own site's settings, e.g. Theme styles.
You can try an advanced setting to see if that helps. Go to Settings -> PDF Embedder, and click the Mobile tab.
Check the box labelled 'Enable if you are experiencing quality issues on mobiles' then click 'Save Changes'.
This will add the following HTML to the head section of every page on your site:
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=0" />
This should have the effect on most mobile browsers of disabling the browser's own zoom feature, meaning all zooming is carried out by the plugin itself. Sometimes, conflicts between the browser and the plugin can cause complications.
Please note you may also need to remove any existing <meta name="viewport" ...> tags from your theme's header.