To combine two designs:

Open the first file, select all stitches or a part of the design and use the menu item "Edit" > "Copy" to copy the selection into the clipboard.

Open the second file and paste the stitches with the menu item "Edit" > "Paste". All stitches will be inserted with a slightly offset and are automatically selected. This makes it easy to change their position after the insert operation. If some stitches of the design were previously selected, they will be deselected. Inserted stitches and their threads are placed at the end of the design.

Save the modified embroidery, it is suggested to use a different file name.