It depends on what you mean by converting classical algorithm to quantum one.
One angle of view can be: Is it possible to run any classical algorithm on quantum computer? If this is a case then answer is yes. Since so-called Toffoli gate is effectivelly NAND gate (in case the controlled qubit is set to state $|1\rangle$ before) and such gate enables to implement any logical function. Hence, you can use universal gate-based quantum computer for implementation of any classical algorithm.
Seconde angle of view could be: Is there a qunatum counterpart to any classical algorithm? In this case the answer is difficult and I am not sure whether it has been resolved already. However, there are some examples of quantum algorithms solving problems we have classical ones for. For instance: Shor's algorithm is used for integers factoring, Grover's algorithm for searching in unordered databases, HHL algorithm for solving systems of linear equations, there are Monte Carlo algorithms useful in finance, Hamiltonian simulations algorithms useful in simulation of quantum systems (the original purpose the quantum computers have been developed for) etc. Moreover, there is a family of so-called quantum annealers. These are single purpose quantum computers implementing quantum annealing algorithm on hardware level.