Can somebody can help me?
Maybe. But how about let's start with some details like, what version of Reader you are using, where you are getting the pdf from, what steps are you taking to open it and what exactly happens when you try.
Adobe Reader DC-from canada.ca a questionnaire-352 KB-I click-a note says
Please wait and if it is not downloading upgrade your Adobe reader-which I did for MAC-and I dit it again and the questionnaire is never there downloaded.
Download the PDF file and open it in Acrobat Reader.
Bernd is correct. You are getting that message because your web browser is not using Reader to try and open the PDF. Many of them have their own pdf viewers and they don't always do a great job at opening pdf files. Especially if they are forms of a certain type. You need to right-click (or whatever the equivalent is on a Mac), choose to save the pdf, open Reader then use File>Open to open the pdf.
Problem is that the right click doesn't offer a save option, so you can't open it Adobe. This is again Canada Immigration, the most unfriendly site in the world. Needs scrapping and starting again.