If Aspose can do it for profit, why can't we do it using .Net or some
other programming
language?
You absolutely can do it yourself if you really want to, exactly the same
way Aspose does it... I.e. open up a PowerPoint file in a hex editor and
work out the file format... That's what Aspose did. Of course, it took them
years and years of cumulative developer time - that's what you're paying for
when you buy an Aspose licence...
The same argument applies to all .NET assemblies... E.g. you don't have to
use ADO.NET for your database work if you don't want to - nobody's stopping
you writing your own library for this... It just so happens that Microsoft
include ADO.NET in the Framework, but don't include a native .NET assembly
for manipulating Office files. Why they don't do this is, of course, a
totally different argument - the simple fact is, they don't...
Big though the .NET Framework is, there are thousands and thousands of
pieces of functionality which aren't included - that's where bespoke
development comes in. You can either write it yourself or use a 3rd-party
solution. Some of these are free and/or open source - others aren't...
Aspose have spotted this gap in the market, and have filled it - you don't
have to use their solution if you don't want to...