The responsibility for purchasing licenses for Foxit Quick PDF Library resides with the company that will have control ownership of the source code after development is done.
As an example, if Company A hires Company B to develop software that utilizes Foxit Quick PDF Library and at the end of the process Company A has full ownership of the compiled software and its source code then Company A is responsible for purchasing the license(s) for Foxit Quick PDF Library and ensuring that the End User License Agreement is adhered to.
However, in this scenario if Company B were to retain ownership of the source code and Company A only received the compiled software, then Company B would be responsible for purchasing the license(s) and for ensuring the EULA is adhered to.
Essentially the company that “owns” the source code for the project should have the licenses purchased in their name.
In all scenarios enough licenses to cover all developers working on the project must be purchased.