I am a LibreOffice user. That is already too much for me, I can do anything with it. Since I am an Ubuntu user, I do not have to even install that, just I am just adding some of its extensions like PDFImport and LibreOffice base, all from Ubuntu repository. I can open, edit and save all the well known documentation formats. But this is not the case for some people:
Let us say, you are an Microsoft Office 2003 user. And somebody keeps sending you .odt or .docx documents. Some of these people are even using OpenOffice.org/LibreOffice but most probably because of their principles, they are sending you .odt documents which you can not open with Microsoft Office 2003. The people who use Microsoft Office 2007 and keep sending .docx documents to Microsoft Office 2003 users are another story, I will try to keep calm, at least for now.
If you are not able to change or educate the sender, and do not want to install another office productivity suite to your system, there is also another solution : Google Docs.
You can upload the document there, and download in another format you can edit. Here is how to do it:
All you need to use Google Docs is a Gmail account. Login to Google Docs, and upload the document.
You can keep the format or let it to be converted to Google Docs format. Do not worry, it does not hurt, you can do both. Here I have had it converted.
Open the document you just uploaded in Google Docs.
Now you can download the file in a format of your choice using the upper-left File menu, as in the following figure:
Mister must-send-in-docx-so-that-nobody-can-open-my-files-but-i-send-them-anyway Microsoft Office 2007 user, sorry, we can edit your files. May be you think that sending .docx files is a kind of encryption, but it is not. We can open them. Come up with something better.