Is it possible to preview a PDF from a container field that is in a portal?
Not quite sure what you mean by "preview from", but you can certainly:
1. place a container field in a portal
2. in FM13 put a popover button in the portal row to open up a larger version of the container field
3. set a scripted button to go to a new layout in a new window with a larger version of the field, large enough to read the contents
4. set up a portal with a one-record view and entirely fill it with your container field
… etc. As often state, there are many ways to do things in FM.
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