Symmetric cipher question

[m999 at vp.pl]

Hello
I have a question. I want to encrypt file that consists of one word for example 'home with AES'. When I did encryption I got file that is 49 bytes. How can I separate my encrypted 4-byte word from the rest of file. I need only encrypted part of my word, I don't want to implement AES on my own.
Best regards
Michael
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