When you download a file named "AutoCAD_2012_Portable_103.rar" from Google search results, you are likely getting one of three things:
Locate the for the free student/educator version Autocad 2012 Portable Free Download 103 - Google
Do not search for "Autocad 2012 Portable Free Download." Instead: When you download a file named "AutoCAD_2012_Portable_103
: Portable versions are often unstable, prone to crashes, and may have missing features. Official Alternatives prone to crashes