Hi Lydia , It is a very common expression used in business letters to indicate the enclosure (inclusion ) of any material ( for example a CV or any business documents ) within that particular sent letter or envelope. Please find enclosed my CV . Please find enclosed the tickets etc

Lydia, It is true that this expression is commonly used in business communication. However, the writer is invoking a poetic license. If I complete the phrase to read "Please find enclosed my resume," then I would find that the sentence does not contain a clear subject. Instead, try using: “I have enclosed my resume for your review."

I guess it means something within the envelope is also sent to you.

Please find enclosed is usually part of a closing of a letter to signal to the reader that the letter contains an attachment. In addition to the letter there is any additional information inside ("enclosed").