What is the ruling on using two different names, one for official documents and another among acquaintances, which leads to confusion when inquiring about the person?

The basic principle is that it is permissible to have multiple names. The Prophet, peace and blessings be upon him, had five names, which he mentioned in his hadith: "I am Muhammad, and I am Ahmad, and I am Al-Mahi (the obliterator) by whom Allah obliterates disbelief, and I am Al-Hashir (the gatherer) at whose feet the people will be gathered, and I am Al-'Aqib (the last)." So there is no harm in using two names, especially if it is to avert harm or bring benefit. However, if the purpose is to commit forbidden acts, then it is not permissible, for the means take the ruling of their ends.