the snagit software only opened eps file extension, but didn't open the ai file? so what is the problem ? does it only open the eps files ? I tried opening the eps and ai but it only opens the eps.
AI files are not EPS files, as of version 9 forward. Older AI files are EPS files of sort, so a version 7 or a version 3 file is an EPS. The newer files however are very complex EPS files and quite many software just can not open them as rasterizing requires a full postscript interpreter. But yes a AI version 3 is EPS.
Newer AI files may sometimes be PDF files though, depending on the settings used.
So to summarize: An AI file may be an EPS, it may be a PDF, or it can be neither.