Attached is the paper or thesis

Please see or refer to the attached

Enclosed 似乎有包含的意思，如在某一个文件或信封中附加、夹带？？

是吧。不过有时法国那边发来带附件的电子邮件时就是用enclosed的。

It is true. For traditional mail, the attachment is physically attached to the letter with staple and the enclosure is enclosed together with the letter in the same envelope.

借用 (移植?)
After the invention of internet, the terms attachment and enclosure etc. are adopted in the communication with email. Another example is “c.c.” (carbon copy), if you use English version of mail box administered by Yahoo or hotmail, you will find “c.c.” although we now seldom use carbon paper (复写纸) to produce copies even in traditional mail.

Each time I write an e-mail to others, I cc to our manager.

Please see the attachment.
The thesis is attached to this email.

我们给客户东西在附件一边就说,"Please see the attached" 或者就是"XXX is in the attached". 就好.

Sometimes, we may want to emphasize that we have done something to fulfill the client’s request, we may be better to translate “您要的”

Suggestion:
The thesis requested is attached.
The thesis requested by you is attached.
The thesis requested together with the relevant information available in our company are attached (for your reference / perusal / retention).

I have also read many times:
Attached please find the……
Attached please receive the……
But I am not sure whether these are formal English.