>how to do encrypt command

As Sergey said, please explain in more detail what do you want to encrypt.

If you want to encrypt a whole table (dbf), the easiest way is probably using Cryptor, a commercial program from Xitech.
If what you wwant is to encrypt/decrypt certain fields (columns) then you can use the Windows CryptoAPI. The FFC has a class (_crypt.vcx) that will show you how to do this. For a more detailed sample, you could also see:
http://feldstein.net/CodeCryptoArticle.htm