Yes, your recipients would've received an email from Adobe with a link to the file that you sent.
If Notify When Recipients Viewed was selected for that file, you should definitely have received notification when your recipients viewed their file. So, it could be that the emails were delivered to a junk mail folder.
You can also see who's viewed your files by logging in to cloud.acrobat.com/send, and clicking the file that you sent. On the right side of the window, you'll see Viewed By, with details of who's viewed your file, and how often.
I hope that helps.