Using Safari 5.1.7, I found a book on a web site that is free and downloadable, but when I click Save As, the Save button is grayed out.

Today (1/11/13) I found an online book, a .pdf file ( a math book from the Univ. of MI) that is advertised as free and downloadable. However, when in Safari I click on File/Save As, the window that opens has the Save button grayed out. The window opens with "Export as ..., and the name of the pdf file appears in the export window.

Any help will be greatly appreciated!