How do I open a PDF posted in safari with another program....Isn't there an "open in" option?

I am using my iPad for school in conjunction with D2L. When professors upload documents to the website (mostly using Adobe) I can open the PDF but only the first page of the document comes up. I have adobe reader on my I pad and the instructions say to click on the "open in" tab and chose adobe reader. However, I have yet to find an open in tab. I have several apps on my iPad including adobe reader, pages and good reader. Please help me find a way to read through these documents.

Thanks!!!!!!!