Duplicate objects (one object sitting on top of another identical object) can be caused a few different things. I see it a lot in customer provided artwork generated in Adobe Illustrator. The Outline Pen effect is the biggest culprit. I always "finalize" my artwork. If there are any outline effects in the artwork I either convert the outlines into their own editable paths or get rid of them.
In CorelDRAW I tend to use the Contour effect to generate real outline effects around letters or other objects rather than using pen tool settings. In Adobe Illustrator I use the Path Offset command rather than the outline effect for the same purpose. That eliminates issues where you have 2 or more identical objects stacked on top of each other when the artwork is imported into a
sign making program like Flexi.
CorelDRAW's pen outline effect and Illustrator's outline effect will waste some of your time when you "flatten" or convert the outline effect to editable paths. You not only have the new path going outside of the source object, but another path running inside of it too. So you have to break everything apart and carefully delete the unwanted extra paths. CorelDRAW's Contour effect and Illustrator's Path Offset effect do not have that issue.