When you open a pdf file into photoshop elements it goes through what is known as rasterization which is the process of taking an image or document that is in a vector format (pdf)
and converting it to a raster (pixel or often called bitmap images) format, which is what photoshop elements essentially is, a pixel editor, so it's not good to actually edit important pdfs in photoshop elements.
Opening them without saving is fine though.
Pdfs can contain both vector anf bitmap data, but the pdf format is considered a vector file type in the eyes of photoshop elements.
That's why you see the dialog come up when opening pdf's into photoshop elements and why you see a dialog asking if you want to save the changes when closing, even though you just
lookd at the pdf.
If you have adobe reader that would be better for opening pdf files.
One word of caution if don't already have adobe reader and that is to look at the page carefully before you download it or adobe will sneak in some virus scanner or something that you may not want.
There should be a checkbox next to the item such as McAfee so you can opt out of the add-on.
I forgot in you one of your posts you asked about the interface font size in pse 11 and unfortunatly it's a fixed size.