Give anonymous web users ready only access

Sure. Give the anonymous role 'access webfm' rights in ../admin/user/access and create a root directory for the anonymous role in webfm settings. Then make sure all the files put under this dir have only the 'Role View/Download:' permission set. Anon users will be able to see and download these files but will not have move/delete/rename rights except for files they own.

Ownership is only possible if the anonymous role is given 'webfm upload' rights in ../admin/user/access. Uploaded files have the default file permissions set in the 'Default File Permissions' setting, however owners of the file have complete right to change the permissions so that others may have more control over the file. The only right the owner of a file can't transfer to other users is the right to modify the permissions. Admins always have complete access to any file.