1. A workflow management apparatus having at least one processor that manages a workflow composed of one or more workflow-tasks for processing documents, the apparatus comprising: a to-do list creation unit configured to create a to-do list corresponding to each user, wherein the to-do list is composed of at least one to-do-task, and wherein a task which is created based on information input via a user interface is able to be registered as the to-do task into the to-do list; a first determination unit configured to determine whether or not there is a current workflow-task to be added to the to-do list; a second determination unit configured to, in a case where the first determination unit determines that there is the current workflow-task to be added to the to-do list and a temporary document is registered for the current workflow-task, determine whether or not the registered temporary document meets a predetermined condition; a registration unit configured to, in a case where the second determination unit determines that the registered temporary document meets the predetermined condition, register the current workflow-task as the to-do task into the to-do list of a user corresponding to the current workflow-task, wherein the to-do list includes both the task created based on the information input via the user interface and the current workflow-task registered by the registration unit; an advancement control unit configured to, in a case where the current workflow-task has been registered into the to-do list by the registration unit, advance to a processing of a next workflow-task in the workflow even if the current workflow-task has not yet been processed; a third determination unit configured to, in a case where a processing of the to-do task registered in the to-do list is completed by a user, determine whether or not the completed to-do task is the workflow-task registered by the registration unit; a notification unit configured to notify a user corresponding to the next workflow-task in the workflow of the completion, in a case where the third determination unit determines that the completed to-do task is the workflow-task registered by the registration unit; and a second registration unit configured to, in a case where a processing of the to-do task for the temporary document is completed by the user, register a document for which the processing was completed in place of the temporary document in the current workflow.