In order to get the certificate, you have to open your documents in Adobe DC. There is a free download for it at https://get.adobe.com/reader/.
Once you have that, follow the steps below.
Click 'Download documents' button in Finmo E-Signing which will open the document in Adobe DC
Go into the document and click on a borrower's signature or an initial in your document
Click on 'Signature Properties' button
Take a screenshot of that and send that to the lender/underwriter. If you cannot screenshot the certificate, after step 4,
Click 'Show Signer's certificate'
follow the steps to save to your computer and attach to an email.