Problem about save text in pdf

[macbookpro]

Hello everybody.
I was able to add text boxes to pdf's attached to emails and then save the pdf and email. Now it tells me "The document cannot be saved.
The file may be read only, or opened by another user. Please save the document with another name or in a different folder."
None of my settings have changed. How can I save the pdf with the same name in the same email attachment?
author: lắp đặt internet fpt

[richell_huang]

When you double click on the pdf attachment, it is saved in temp folder and the file is read-only, so you can not save it directly, but you can press save as button to save it to your local disk.