No, this is not legal. Current license fee:
One-time license fee - $ 5,000
The following libraries are owned by Adobe and you need to obtain any license if you want to sell it for commercial purposes.
http://www.datalogics.com/products/pdfl
The following files are wrappers and there is no need for a wrapper license:
AxInterop.AcroPDFLib.dll
Interop.AcroPDFLib.dll
But if you download both of these files from anywhere on the Internet, it is not practical to sell them to your customers. Source files
AxInterop.AcroPDFLib.dll
Interop.AcroPDFLib.dll
Needed, and then you need a license. Please note using http://wpfpdfviewer.codeplex.com/ to read PDF files. It is not free for commercial as it seems.
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