Thunderbird does not open Word documents. Your only option is to open two windows side by side with the email in one window and the document in the other one.

Airmail, thanks for your prompt reply.

Is there any other way I can prove that this particular attachment is exactly what I received in the email ?

You have the original email and attachment don't you?

yes, but in Court, I do not know if the judge will accept it as evidence if I showed him the email and its attachment on my laptop

As I understand it you have received two versions of the document, an earlier and a later one. I assume you have saved them both. I know nothing about your computer system and software, they are all different. But in many it is possible -- in a wordprocessor and/or in a file explorer -- to display document properties. In my wordprocessor, for example, I can find the date when a document was created and when it was last edited; by whom; how long the editing took; and so on -- a stack of information. All of this information is recorded and updated automatically by the wordprocessor as the document is written and edited, and most users don't know it is there. Depending on the nature of the documents you have received, and on the software you have available, it may be possible for you to find similar information, and thus to demonstrate which version of the document was the earlier one. Whether a court will be convinced by this I have no idea but it's all I can think of to help you.

Legal advice is out of the scope of this forum.

Thank you all to everyone here who tried to help.

I hope no one will ever be in my position where I am doing everything I can to prove the truth against people who lie and forge documents...

It is in the word document summary that you will find the information you seek. I have attached an example image.

The other thing you can do it take the machine to a computer technician and get a statement from this person as to the content of the mail and it's attachments. Experts tend to be believable before the courts. But as Airmail said. Legal advice is beyond the scope of this forum. I wish you luck.

For the future, be aware that digitally signed emails prevent modification of an email after it is sent. S/Mime certificates are available from many authorities and bring to an automatic conclusion any discussing about an email being edited after it is sent. It can not be done without voiding the signature. It is just a shame that most people simply do not use the technology.

Thanks a lot Matt