cannot download documents that are attached to received emails
And why is ask.libreoffice.org with respect to https://wiki.documentfoundation.org/Ask/Getting_Started the right place to ask this question (which btw. is only a question if implicitly reading a How do I … fix)? Refer to your email client’s documentation.
Did you mean that you can not open or access documents that are attached to emails? Please be specific.
… and give LibreOffice version and operating system (if it’s not a problem of your mail client anyway).
Please edit your question to provide details, do not use the Answer field.