To create a link to a PDF file which you have uploaded to your site, right click on the 'view' link, select copy link address.
E.g. The address of the pdf file attached to this page is:
Now go to the page where you want the link, edit the page, highlight the text where you want the link, click on the LINK button in the editor, select 'Web Address' and paste in the link copied in step 1 above
It is also possible to 'drag and drop' links from the same or another tab or window.
If you want the link to open in a new tab/window, when in the page editor click on the link, select 'change' and check the box next to 'Open this link in a new window'
Alternatively, use the iframe gadget to embed the PDF viewer directly into the page (using the same link as above) as shown below
Include gadget (iframe)
Or you can use Mori's PDF wrapper gadget to embed the PDF into the page as shown below.
Note: If your file is hosted on a Google Site, copy and enter its Download link and make sure the host Site is public.
Google Docs Viewer
Or if you store the document in Google Docs, you can use the 'File > Embed this pdf file' code generated by Google Docs (the document must be shared as 'Public on the web')
Provided it is available publicly on the web, you can use Google Docs viewer as described at