Once you’ve received your document and are viewing it in Acrobat Reader, all you need to do is select the File option from the pull down menu and choose Save As. Type in a filename which relates to the actual document and be sure to include the .PDF extension so that Acrobat Reader will recognize the file type should you wish to view the document again.
It is suggested that you save any downloaded file prior to printing.
Please keep in mind that it is against copyright law to make or forward copies of articles to others. It also tends to gobble up considerable amounts of hard drive space by keeping old documents around. A good practice may be to delete any documents once your papers or classes are finished.