Question:

Why is a user unable to zoom in on a PDF when the Disable Actions Field is blank for the Key Message?

Answer:

The CRM Mobile Applications enables the Zoom functionality on PDF content when the width of the content is greater than or equal to the height.

Example: 

A 1080x1920 pixel PDF does not allow for zooming. This is because the width (1080) is smaller than the height (1920). A 1920x1080 PDF allows for zooming by default. 

Related Documentation:

CRM Help Documentation: N/A