No, not every substance can be converted into a magnet. Why do you say that ? May I know please ? Are you asking a method to convert every substance to magnet ,or are you asking how it can be converted to magnet ?
Not sure the context of your question, but fundamentally every electron, proton and neutron is a tiny magnet. Most substances do not show coordinated magnetic behavior of the electrons (the strongest magnets) at room temperature. ... but I suppose, if you got down to one molecule of a substance and made sure it had an odd number of electrons (the electron magnets tend to pair and cancel themselves out), you could in theory convert the substance into a magnet.