@rhaynes999 - As you have probably determined, this is not possible.

If you only need a rectangular shaped portion of the PDF, you could:

1. Extract a page
2. Convert the page to am image using the Copy as image action (and then paste it back to the board):

   

3. An d then crop the image:

   

While this may not be your ideal solution, you could add this as an Idea in the Wish List category by following the guidelines here: Wish List: Everything You Need to Know.

If you do create a Wish List Idea post, I would also recommend that you post a link to it back here, so that future readers of this post can quickly get to and vote for your Idea.

Lastly, don't forget to vote for your own Idea.

Thanks for this reply.  On the ipad, how do I paste it back to my board? 

Not sure. Never used an iPad.