If you want to encrypt a .pdf file, there are mainly the following methods:

In Adobe PDF Reader 3.0 or later, open a .pdf file and select "Encrypt" in the "File" menu. ". After selecting the encryption method, the file will be encrypted. Since the encrypted part is the code part of the file, copying and pasting will not affect the normal use of the file.

Add a valid digital signature to the file. The file can still be transferred normally, but if the file is modified, the digital signature will be broken.

Restrict file read permissions. If the file read permissions are set in the Windows operating system, the file will lose the restriction as soon as a user successfully copies the file and pastes it to another computer; if the restriction is in Adobe PDF Reader, the restriction will still be in effect after copying and pasting.

From the above, it can be seen that unless encrypted through the Windows "single-user read permission restrictions" feature, the file is copied and pasted, the file will remain encrypted and not be damaged.