Some students have reported problems with the document or presentation files uploaded to this website.
This is probably due to the fact that you have been using an older version of MS Office but it is no big problem to fix. Just follow this link, choose the language of your MS Office installation (most likely, English or Greek), click the download button and run the file once it is on your computer. It will upgrade your MS Office installation so that you may safely open and save documents in the latest file formats such as .docx, .xlsx, .pptx, etc.
To make sure you understand what you need to do, just watch this video:
If you haven't got MS Office installed on your computer, why don't you download the free version of MS Office? It will not allow you to edit or save any files but it will allow you to view any file you download. Just follow these links and download the programs you need:
Now, if you want to be able to view, edit, and save MS Office files and more but you don't have MS Office on your computer, why pay for it when you can get LibreOffice for free? Just follow this link and you can download and install it in no time.
If you want to learn more about LibreOffice, you can watch this video and many more on YouTube.