Updating regerences with PMID

I am using endnote x6 on windows.  I have imported a numbers of PDFs and most have found appropriate references.  Some have not.  For those, it was suggested by a colleague that uses endnote on his Mac that I paste the PMID number from PubMed into the accession number field, then under references click find reference update.  On his version this updates beautifully, on mine it says it can’t find an update.  I’ve tried with numerous PDFs and it doesn’t work.  Has anyone gotten this to work on their windows version, or have suggestions an easy way to update references when they aren’t found with uploaded PDFs?  Thanks!