Bereishis 37:12:
וַיֵּלְכוּ אֶחָיו לִרְעוֹת אֶת צֹאן אֲבִיהֶם בִּשְׁכֶם.
Rashi there says (as I understand it) that we cut out the word es (אֶת) because they only went to to feed their own sheep. If so, then why does the Pussuk mention צֹאן אֲבִיהֶם ?
Sifsei Chachomim explains that they went to pasture themselves, and their fathers sheep happened to be there.
Rashi means that although they obstensively went to pasture their father's flock, the Torah hints to us that their main intention was to feed themselves.
The Terumas Hadeshen in his sefer באורי מהרא"י explains as follows:
We can explain that the logic behind this teaching is that although some words are dotted to teach us that there is hidden meaning, nevertheless, the hidden meaning of the word never completely leaves the simple meaning, because the word is certainly written. Therefore, in this posuk the hidden meaning is derived from the fact that the root of the word את is אות which forms the words אותו (him/it) and אותם (them).
And we find that these words sometimes mean 'himself' or 'themselves', like in the posuk concerning the nazir in Bamidbar(6,13) “This is the law of the nazir: on the day that the days of his being a nazir are completed he shall bring him (יביא אתו) to the entrance of the Tent of Meeting” the phrase יביא אתו means "he shall bring himself", as Rashi explains. And he adds that this is one of the three places in the Torah where R. Yishmael teaches that the word את and its suffix are understood to be reflexive, the other two places being in Vayikra (22,16) “and so cause themselves (אותם) to bear iniquity and guilt”, and in Devorim (34,6) “and he (Moshe) buried himself (אתו) in the valley”.
Therefore, here also the hidden meaning is that they pastured themselves.
The full English text can be found here
I have no source for this: it's my own thought. I've heard that letters with dots are interpreted as if absent. (Citation needed, as they say over at Wikipedia. On the other hand, that seems to be the premise of the question, too.) If es were absent from this verse, it could be read "The brothers went to pasture. The sheep/goats of their father were in Sh'chem." which could imply they were pasturing themselves.
But of course that's a d'rasha: the plain meaning is that they were in fact pasturing their father's sheep/goats, which is why the verse mentions the latter.
