Sorry you are having difficulty downloading the Adobe SendNow Desktop App. When you click on the yellow Download button from this page https://www.acrobat.com/sendnow/en/desktop-download.html, you should see a popup dialog that looks like this attached image. You can click on the Open button to start the installation. It is possible that the dialog is displaying behind your other open windows or applications. You may want to close your other windows before you click on the Download button. If this doesn't work, please provide more details as to your problem and also let us know what browser and OS you are using.
Adobe SendNow Product Manager
Could you let me know what OS and browser you were using when you tried to download the Adobe SendNow desktop application? Do you have Adobe AIR installed on your system?
Jyh-Jiun L. Tseng
Adobe SendNow QE Engineer