My husband owns some books that were in his house when he was a bachur. One of the books has a list of kabalos and draft of a letter that one of his siblings wrote. From a quick glance at the papers, it would probably be very embarrassing to return it to his sibling. Are we allowed to throw out the papers?
It is very hard to know this, because the sibling might in fact want the papaer back, (for example, regarding the paper of his kabolos). The best thing would be to put it back into the sefer and just send the complete sefer to him, and write something very mattter of fact such as, “I found your sefer in my house”. This way he wouldn’t know that you even saw the paper.