Hope you are doing well. I am sorry for the delayed response.
The error message that you get as shared in the screenshot is not something that is happenign because of Acrobat Reader Mobile but looks more like an issue with the browser and file access permissions.
You might want to try to use the share option that download. Try using the share option at the top right-> scroll down on the menu that comes up next and select the option save to files.
Then once it is saved, you can locate the file and then open it in Acrobat Reader Mobile.