When opening a 3D PDF file, it may be desirable to set a preview image prior to the user enabling 3D display. Many scientific publications use web-based pdf viewers and 3D figures may appear blank.
On the Annotations tab, open the “Text Parameters” group. Here there is an optional feature [x] AltImageUnder3D. By selecting this option, and using the “Change” button, an image file (PNG, JPEG, TIFF) can be specified which will be shown in case the PDF is viewed by a web browser or some viewer that does not support 3D.
If such a preview image is specified, there is also another option on the PDF 3D View tab, for “Activation Mode”. Normally it shows the 3D immediately, with the “On Visible” mode. This can be changed to “Manual”, so the preview image is always shown and the user has to click to activate the 3D (if available on the viewer).