How to enable SharePoint checkout when opening a PDF form?

When opening a PDF form saved in SharePoint, users were prompted whether they wanted to download or check-out/open the form.  Users could check-out, sign, and check-in the form from the browser.  Then we started getting notices that this feature had disappeared.  Users had to download, sign, and re-upload.  Contacted Microsoft who stated this was caused by an Adobe update.  We were able to change some configurations to allow users to open and sign forms in the browser but the check-out option is still missing.  Users can check-out as a separate steop before opening the form but users are still asking us to try and bring back this feature.  Does anyone know how to reinstate this?