A .ydr on its own streams but is not a placeable object: maps, CodeWalker and many scripts need its archetype in a .ytyp. Prop to YTYP reads your .ydr and .yft files, fills in their bounds, LOD distance, texture dictionary and flags, and writes one .ytyp for all of them.
You get a FiveM resource with your props, the .ytyp and the data_file line in the fxmanifest. If a model was made somewhere else, its size and textures are checked before you download.