1. in adobe pdf reader version 3. or above, open a. pdf file and select "encrypt" in the file menu. After selecting the encryption method, the file will be encrypted. Because what is encrypted is the code part of the file, copying and pasting will not affect the normal use of the file.
2. Add a valid digital signature to the file. The file can still be transmitted normally, but if the file is modified, the digital signature will be destroyed.
3. Restrict file reading permission. If the file reading permission is set in the Windows operating system, as long as a user successfully copies the file and pastes it on another computer, the file will lose its restrictions; If it is restricted in Adobe PDF Reader, the restriction is still valid after copying and pasting.
4. As can be seen from the above, unless it is encrypted by the function of "read permission restriction for single user" provided by Windows, the file will remain encrypted and will not be damaged after being copied and pasted.