How can i convert these two files from .STL mesh to solid file?

It is not smart at all, to say "You cannot" How can you be so sure...
Please don't get me wrong Barta but in our days everything is possible!!!

I found many times that a solution to any potential limitations of a software can be overpassed by an add-on so... The key is a tool to do the job!!!

Therefore I will post a Tutorial that can be considered as a solution to Nuno's problem...

http://grabcad.com/questions/tutorial-convert-stl-mesh-to-solid-file-in-autodesk-inventor

However,
It is good to have open mind as there might be another easier way to follow other than my post.

Instructions
1
Launch the SolidWorks project you wish to use to import an .STL file. Click the "File" menu and choose "Open."
2
Click "(*.stl)" from the "Files of type" drop-down menu, then click "Options." Three main options will display in the "Options" dialog box.
3
Click "Graphics Body" if you wish to import the STL file as graphical data only. Click "OK" to confirm.
4
Click "Solid Body" if you wish to import the STL file as a solid body. Click "OK" to confirm.
5
Click "Surface Body" if you wish to import the STL file as surfaces. Click "OK" to confirm.
6
Click the STL file you wish to import and click "Open." Allow for the import process to finish.