FOund part of the problem  : the not showing of the document was because my browser ( chrome ) does not run unsafe scripts ( which according to Chrome this is ...)

By accepting the unsafe script it shows the pdf document.

Not possible to upload a ppt. Is there a way to do that ?

It can be a good idea to create a database with DEMO data so you can learn how Odoo works.  

When creating the database, you will see a box "Check this box to evaluate Odoo" and that will install the demo data.

You will then see on the Presentations Tab of the website:

And then, for the UNPUBLISHED (private) channel:

Telling us you have "tried everything" gives no information on what modules you have installed, whether you were able to create  a private channel, if you get any errors.  

Perhaps you can explain what you have tried, as it is hard to guess what went wrong.