Signing a pdf

[#1]

I need to sign a pdf doc. I am using Adobe Reader DC. I selected tools and "fill & sign". A "sign" icon appears at the top, but it is shadowed in gray and nothing happens when I try to click on it. What should I do?

[#2]

After selecting the tool "fill & sign", just move your mouse on the PDF file. Did your mouse become an "IAB" patten? If yes, just go anywhere you want to sign and start typing.