During your research on a topic, you no doubt discovered several examples illustrating the topic. In each section of your paper, add an explanation of one of these examples that supports that topic. This technique can easily add a page or more, since you'll often need to give a little background on the example as well. If you are discussing the ethics of altering news stories and whether or not Photoshopped illustrations should be allowed in magazines, newspapers or websites, then add in the story of Allan Detrich, the "Toldedo Blade" photographer who was fired for Photoshop violations. You can be as descriptive as necessary -- tell about specific photos, describe the controversy, add in reactions from other photographers -- all with little additional research on your part. Be sure you cite your sources and avoid plagiarizing -- use your own words.
Using direct quotes requires you to introduce the quote, add in the actual quote, then explain what the quote means and why it supports your point. This is lots of fluff for one supporting point. Additionally, APA, MLA and other style books require that a direct quote of length (often two lines or more, but check the stylebook you're using) need to be indented and set apart by double spaces before and after. It's not your fault this also takes up lots of space. Using too many direct quotes will invite critique of your inability to analyze the text, but one per supporting point will give you points for research. Again, remember proper in-text citations.
Part of writing a research paper is repetition -- saying what you've said before, but in a different way. For example, if you have failed to write a thesis sentence or a concluding sentence for each main point, do it! Not only does this add length to your paper, but it makes the paper more readable, make more sense and get a higher grade. So in each section, tell the reader what you're going to say -- for example, "Since walking is such a simple exercise, more people are likely to continue it for longer periods of time." Then the next section should give all the supporting data, and at the end you should write a sentence or two explaining how you've illustrated that old people, out of shape people and anti-exercising people all benefit from taking up a program of walking.
If you haven't already, write about the arguments opposed to your point of view. Don't give them equal space with your arguments, but acknowledge then refute them. You've doubtless run across these opposing points of view in your research; add length to your paper by spelling them out, telling about the main proponents of those points of view and explaining why you think they are wrong.
If you are desperate for time and need only a slightly longer paper, change the font to Palatino Linotype. It has the look of Times New Roman, but is slightly larger. It gives you a little added length without looking as though you are trying to cheat your way into the required pages. Using Arial or Century or using a bold font will scream to your teacher "I had nothing to say and I'm hoping you won't notice." They'll immediately take notice and will look for shallow arguments and lack of depth in research.