Hi @Anonymous,
Thanks for posting!
There is definitely a way to do this! The first step will to be to open the design that you want to build everything in, which will most likely be your main body piece. Then you can either drag in the file you want to bring in from the Data Panel to the design or right click the component file in the Data Panel and select "Insert into Current Design".
This will create a component in your body design that is referenced to the original external component file (if it was brought over from the same project folder). This means that you can go ahead and make changes to the original component design and when you update the the main body design file, the inserted component will convert to its new design. The referenced file can be indicated by a chain link image next to its name in the browser tree. If you right click on the inserted component, you will see options for "Get Latest", "Choose Version", and "Break Link".
You can insert a component from another project, but in this case that component will not be linked to your body design.
More information on inserting a component here.
Please accept as solution if my post fully resolves your issue, or reply with additional details if you have more questions.
Thanks!