First test it with Acrobat (paid product) NOT Acrobat Reader. Does it work? If so you can apply to Adobe for a license to make plug-ins for Reader. If they like your idea and accept your application you can pay the fee and receive the key needed to make Reader plug-ins.
see.. after .api file is generated, i put it under the adobe<plugins folder.
then i opened the acrobat reader DC to see if that plugin was added. but it is not
No, use Acrobat. Acrobat Reader is not suitable for your development, even if you eventually intend to pay thousands for a Reader plug-in license.
ok. can you please send a link to get acrobat
Duplicate, answered elsewhere (how to buy Acrobat).