Adobe Acrobat — Using Separate Windows
By default, Adobe Acrobat/Reader DC opens multiple PDF files in a tabbed interface, within the same window. This means you cannot Alt-Tab between documents or place different documents on different monitors.
To change this behaviour:
- Go to Edit → Preferences.
- Click General on the left-hand pane.
- Untick Open documents as new tabs in the same window.
- Click OK.
- Close Acrobat.