Do I have to pad the image for frequency filtering?

I read on the book "Digital Image Processing" Gonzalez-Woods paragraph 4.6.3 that for filtering an image in the frequency domain we have to pad the image with zeros due to the periodicity. In this way after the filtering we get the right result. Now the questions:

1. I have to pad only the image or also the filter?
2. Since in matlab the fft2 returns only one period we really have to pad the image in matlab. Because my impression is that if the fft2 returns only one period, actually, we don't have periodicity. It is right?
3. I tried to filter an image with a butterworth high-pass filter (n=2) two times: one padding the image (not the filter) and another without padding (neither filter nor image). The two results are here: http://www.flickr.com/photos/63036721@N02/sets/72157626778171074/detail/ Is possible to see that in the padded image the borders are different than in the nopadded image. It is right?
4. If I don't pad the image the result of the filtering is different only in the borders or also in the content?

Sorry for these long questions, but this a doubt that I am not able to solve. Thanks