If it’s something like Orphan Laine’s Letter, then when you drag it from your inventory to open space and let go, you get a pop up saying “Do you really want to delete (name of item) (here, Orphan Laine’s Letter)?” There is a text entry box in the window. Click in that box. Type in the (name of item) exactly as it appears in the pop up box, capital letters and all. Then click “Yes” (just hitting Enter won’t do it).
