403 Error

I have uploaded a few items files in the form of PDFs, but some PDF files seem to generate the following error although they are under 64 MB.

Thoughts?

Forbidden

You don't have permission to access /wos/admin/items/add on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I'm not sure of what would cause a 403 error when uploading a PDF like that.

This sounds like an error coming from Apache, so there may be some server setup on a lower level than Omeka that's rejecting those uploads.