: Create a 2D plane and use the Extrude tool to give it a very small thickness (e.g., 0.1mm) to make it a "solid" object.
If you are looking to create a "solid" file structure for your mods using a .7z archive: Archive Method : Use 7-Zip to compress your mod files. ME2.7z
If you are trying to create a "solid" (3D) piece of paper in modeling software: : Create a 2D plane and use the
: In programs like Vectorworks , use the Shell command to turn a flat surface into a solid with specific thickness. ME2.7z