There are 2 similar ways to do this.
Method 1.
First make sure you are in the design workspace then activate the flat pattern you need in the drawing. Now use the workspace drop down to select Drawing -> from design. This will open up a dialog with the top section grayed out (more on this in method 2). You now need to use the destination drop down to select the drawing you want the pattern on, This will be 'UNTITLED' if you have not saved the drawing yet, after setting that a new drop down appears with which you need to set the sheet (if you have not named them yet then it will show sheet 1, sheet 2 etc.). Now press OK and fusion will change to your drawing and the flat pattern will be on you cursor ready to drop where you want.
Method 2.
This way does not require you to activate the flat pattern. Back again in the design workspace use the workspace dropdown to select drawing -> from design, when the dialog pops up uncheck full assembly then click the component you want the flat from, this will give you a new drop down to select from folded or flat (this was the grayed out bit from method 1), pick flat. the rest is the same as method 1 (set destination).
Hopefully this is what you wanted.
