I have heard that in order to open a matza box on Shabbat one must tear the box in a destructive manner so it can't be used again. However, since once the matzos are finished the box is thrown out is it okay to open it on Shabbat without tearing the box in a destructive manner?
Per Rabbi Doniel Neustadt a box which is not reused may be opened on Shabbos even in a way that does not destroy it. He brings this in the name of Rabbi Shlomo Zalman Auerbach. He does mention that there are dissenting opinions to this that hold it is forbidden.
But it is permitted to open a cookie or cereal box or bag, even if one does not immediately empty out its contents and even if the box or bag is not destroyed in the process. It makes no difference if the box is made out of cardboard, plastic or paper, nor does it make a difference if the box contains food or something else such as medicine, clothing or toys. It is only prohibited to open a container which is made of strong, long-lasting material such as a barrel or a corrugated box which might be reused in the future.
- Rav S.Z. Auerbach in Tikunim u'Miluim 9:11 and Shulchan Shelomo 314:7-5, 6. See Binyan Shabbos, vol. 2, pgs. 145-149, for a comprehensive review of the entire subject. There are dissenting opinions who are stringent and forbid opening all boxes or bags; see Knei Bosem 1:22.