Where should I enter License Key I got after purchase?

The license has to be activated just once. You can activate it through command line:

ispringsdk.exe a <license name> <license key>

Also it's possible to activate it via CodeBuilder. To do it, please, proceed to iSpring SDK CodeBuilder ---> General tab ---> License.

The product license data are required during the products use and must be passed to iSpring SDK each time the conversion is performed.

You can use the following samples:

[C# example]

PresentationConverter pc = new PresentationConverter();
pc.LicenseName = "John Smith";
pc.LicenseNumber = "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX";
// ...
[/C# example]

[VisualBasic.NET example]
Dim pc As PresentationConverter = New PresentationConverter
pc.LicenseName = "John Smith"
pc.LicenseNumber = "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX4"
' ...
[/VisualBasic.NET example]

[PHP example]
$pc = new COM("iSpring.PresentationConverter");
$pc->LicenseName = "John Smith";
$pc->LicenseNumber = "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX";
// ...
$converter = null;
[/PHP example]

[Java example]
PresentationConverterFactory pcFactory = new PresentationConverterFactory();
PresentationConverter pc = pcFactory.createPresentationConverter();
pc.setLicenseName("John Smith");
pc.setLicenseNumber("XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX");
// ...
pcFactory.release();
[/Java example]

[C++ example]
CoInitialize(NULL);
{
CComQIPtr<iSpring::_PresentationConverter> pPC;
pPC.CoCreateInstance(__uuidof(iSpring::PresentationConverter));
pPC->put_LicenseName(CComBSTR(L"John Smith"));
pPC->put_LicenseNumber(CComBSTR(L"XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX"));
// ...
}
CoUnitialize();
[/C++ example]

[VBScript example]
Set pc = CreateObject("iSpring.PresentationConverter")
pc.LicenseName = "John Smith"
pc.LicenseNumber = "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX"
' ...
[/VBScript example]

[Command line example]
ispringsdk.exe s --license "John Smith"
"XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX" <ppt> <swf>
[/Command line example]