"We seek for truth wherever we may find it. The Prophet Joseph Smith taught that “Mormonism is truth. … The first and fundamental principle of our holy religion is, that we believe that we have a right to embrace all, and every item of truth, without limitation or … being … prohibited by the creeds or superstitious notions of men.”

Yes, we do have the fulness of the everlasting gospel, but that does not mean that we know everything. In fact, one principle of the restored gospel is our belief that God “will yet reveal many great and important things.”

... So we continually seek truth from all good books and other wholesome sources. “If there is anything virtuous, lovely, or of good report or praiseworthy, we seek after these things.” In this manner we can resist the deceit of the evil one. In this manner we learn the truth “precept upon precept; line upon line.” And we will learn that intelligence cleaves unto intelligence, and wisdom receives wisdom, and truth embraces truth."

Elder Uchtdorf

http://www.lds.org/broadcasts/article/ces-devotionals/2013/01/what-is-truth?lang=eng