I asked ProConnect Help (twice, to different agents), and they both looked at the return with me on SmartLook, and both confirmed that ProConnect supports E-Filing Form 5471, as the PDF form was generated within ProConnect for the IRS, and no critical diagnosis appeared to prevent e-filing.   

The tax return was a C-corp return with a 9/15 extended deadline.    

I wonder if I should leave it as it is, or should I still file an Amended Return with no changes on income and deduction, and just attach the PDF form stating the attachment was accidentally omitted?