I have a template file that users continuously save over the existing file. Is there a way to lock a file in sharepoint so that it cannot be saved over and users are forced to "save as"?
Make a new content type for your document library based on the Document content type.
In the advanced settings of the content type, you can link to an existing template (stored in the Forms folder of the library which is hidden from users) or upload a new template.
And if you only want users to add documents with this template, remove the Document content type from the library.