Which security role is necessary for users to upload and download documents without modifying security settings?

The necessary security role for users to upload and download documents while maintaining the ability to interact with the document's security settings is the Editor role. This role provides users with the ability to manage documents, which includes uploading new documents and downloading existing ones. Editors can engage with the documents at a level that allows them to perform these actions without altering the overarching security configurations.

Other roles may have restricted capabilities. For example, the Viewer role typically allows users to view documents but does not grant the permissions required for uploading or downloading. The Admin role generally encompasses broader operational permissions, including security settings management, which is not aligned with the specific need to upload and download without altering security. The Contributor role might allow certain interactions, but it may not specifically allow all the capabilities associated with document management in the same way the Editor role does.

Thus, the Editor role stands out as the best fit for the requirements mentioned in the question.