Hi there,
Using dynamics PDF can be tricky sometimes with the flowable contents...
If you put radio buttons inside a subform which is set to Flowed content, the radio buttons will flow from top to bottom,
in other matters, if you want to set the radio buttons to flow from left to right (horizontally) you will need the change the flowed content.
Subforms content can be set to : Positioned or Flowed.
When using the Flowed option, you have 2 more options available to you within the flow direction property, which are "Top to bottom" and "Western Text"
if you change the flow direction to "Western Text" any objects within that subform will flow from left to right
I hope this help!