cannot download and save pdf files

All of a sudden I cannot download PDF files. This has been working for for years. Regular downloads of other file types still work without problem. But when I click on a PDF link, I get a blank new tab/window with a status of Done and nothing else happens. I have all the PDF helper apps set to use Adobe Acrobat Pro to open all downloaded PDF files. When this started, I changed all the helper apps to Always Ask. No change... blank window... no download... no popup to ask... This happens on all websites I try to get PDFs from.