is it possible to fit the pdf inside the container(style book)?
I have just had a quick go at what you doing.
I cannot see an option to make the document to “Fill” the container of the Document Booklet.
Unless someone from support has the answer, I think possibly you will need to resize the document you are wanting to show in the booklet.
I resized the document and it’s work
It looks like this issue was solved. But I was thinking that if what you were after was to eliminate the white space above and below the placed PDF, you could set the container background color the same as the layer background. This may or may not work depending on what your background is (solid color vs. image or gradient). If this approach solves the problem, though, it could save you having to resize (and perhaps cropping out something you’d rather retain).