It's not impossible to do in every case, but there are limitations that may either keep this from working for you or may result in a layout design that is more complex than simply using two layouts for the two platforms with a script that detects which device has opened the database file and then selects for the user the appropriate layout.
Tricks you can use:
Learn how auto-size anchors work. If you set left and right anchors for a layout object, it will "strectch" to a wider size when the window expands to a wider size. If you set just a Right anchor in place of the default left anchor, the object will slide to the right as the width of the window increases. If you select neither left or right anchors, the object will neither slide nor stretch, but as the window width increases, the added space is equally divided to the left and right of the object keeping it in the same position relative to the center of your layout. You can also place an object such as a field or button underneath other objects so that they are hidden from view (I sometimes use a rectangle colored to match the layout back ground to hide such an object), but with the right or bottom anchor selected instead of the top or left anchor. When the window increases in size due to opening on the desktop or due to rotating the iOS device from portrait to landscape orientation, the anchor pulls the object into view from its hiding place. Portals with top and bottom anchors set will stretch to reveal more portal rows as the window height expands.
The above tricks can work, but the "layer cake" of objects hidden behind other objects. can be difficult to work with when the need arises to redesign your layout. And some changes you might want to make to your layout using these techniques just don't work. Try getting a "grid" of more than 3 columns of layout buttons, for example, to stretch evenly when the window resizes to a wider size.
Other layout issues that you will encounter is that some layout controls are best suited for a mouse and other controls or control sizes are better suited for a finger. So you may find that check boxes, radio buttons, layout buttons etc don't work as well as you'd like on the iPad as they do on the Desktop without resizing them to a size that may not be what you like for desktop users.