What is the ruling on working for a mobile software company that relies for its profit on advertisements which may contain impermissible content, the content of which cannot be controlled, and the profit is based on the number of user clicks on the advertisement, while it is difficult to obtain profit by other means?

If you are unable to control the advertisements that advertising companies place in your programs, and it is highly likely that there will be prohibited advertisements, then it is not permissible for you to contract with advertising companies. This is due to the potential for assisting in sin and transgression by promoting forbidden things.