Big Business lets you drag in files, like a PDF, to the Docs folder on any transaction. This is handy for saving PO.pdf with your new Order. It just needs to be its own file. If it's not, drag out of the original application to create a separate you can then drag in.
To create a separate file, drag out:
one page from a pdf
one email from an email prgram
one attachment from another app
Drop in a convenient location like Downloads or Desktop.
For example, drag one page from a multi-page pdf and drop it in your Downloads. Then open your Downloads and drag the one page to the Docs folder in Big Business.