Hi Rene,
- When you ask for PDF files that are displayed (like an image, I suppose), have you tried adding them as a resource (link to a file) and them setting them to be displayed in the same page? That way, when you click on its name, whatever is on the PDF will be displayed on the screen.
You can also try doing a print screen of the PDF, save it as an image and then show it on the course page, but that might bring about other problems, since an image doesn't allow for the same things as a PDF (like searching text, copying, editing, etc.). - When you choose to add an image you must either select it from the folder you uploaded it to, or browse your files, select the image, upload it to Moodle and then select it. The URL field indicates the place, in Moodle, where the image was saved. Alternate text is the like a tooltip. It's the text that appears when you go over the image with the mouse.
- The size of a file isn't measured by its number of pages, but by the space it occupies in the computer. You can add it as a resource (link to file) so that the student can download it. Anyway, if it is a Glossary, why not use Moodle's glossary activity instead? You can import the list of terms from a XML file.
Resources can be downloaded, as well as displayed on the course page. That is the case for linked files, and any other files that might be saved in displayed folders, for instance.
Hope it helped!