1) Open the attached file "Dim_3.tcw"
2) Goto File --> Save As
3) Choose "Save as type: DAE" from the save as dialogue box.
4) Press Save and then close file ( File --> Close )
5) Now open the DAE file which was saved by File --> Open and selecting "Files of Type : DAE" and then choosing the file "Dim_3.dae".
Compare both drawings, objects are missing in the DAE file.
Reason: DAE (COLLADA) file format is 3D graphics format that does not store 2D graphics. The file contains 2D objects which are not catered by DAE format by default.