You may already know that if you double click inside a viewport that is on a layout tab you will be able to work in model space even though you are in paper space. This is known as working in “Floating Model Space.” But you also may know that if you do this and your viewport is NOT locked, you will mess up your viewport scale when you zoom in & out and when you pan.
Fear not – here is a way to be in paper space and activate an unlocked viewport and still be able to work in model space and not mess up your viewport scale:
Simply double-click the frame of the view port. You will be thrown into what looks like model space but you will notice that there is a red striped frame around the drawing area. You can also use a command to achieve this. It is VPMAX <enter> then select the viewport border to maximize it. When you are finished, the command to exit is VPMIN <enter>. There is also a new button at the bottom of the status bar that has the similar red stripes around it. Click on this to exit as well.