When Login window pops up in internet explorer please disable "Adobe Acrobat SharePoint OpenDocument component" by doing the following:
Procedure 1 : Click on Tools > Manage add-ons > look for "Adobe Acrobat SharePoint OpenDocument" click on it once > Click Disable then try and open the Form/document again. If you can't find the "Adobe Acrobat SharePoint OpenDocument" please perform procedure 2.
Procedure 2 : Click on Tools > internet options > Advanced > Reset > tick the "Delete personal settings" box > Reset > Close Internet Explorer (IE) > open IE again then CAA site and test by opening the forms/documents. A notification may pop up at the top of the browser that requires a user to run an Adobe Pdf fill add-on > allow the add-on to run then repeat procedure 1.
If the problem persist after performing procedure 2 then repeat procedure 1 and now the "Adobe acrobat SharePoint OpenDocument" will be there, just disable it.