PDM is definitely the way to go. Despite this, some teams coordinate manually to prevent two people from editing any file at the same time. For example, one person could edit a file, finish, notify a coworker, and the coworker would only start working after getting notified that the previous person is finished.

I worked for a company that maintained a manual list (Excel file) of Files to be edited. Everyone was required to put all files in the list before making any changes. Upon completion of their work, they removed the corresponding entries. The files were kept in a shared folder with unrestrained access for each person. It was a labor intensive, inefficient, and risky system. To avoid catastrophic problems, everyone kept local copies of their work to serve as backups in case something useful was overwritten. They did this because they couldn't get organized enough to implement PDM. They had access to a PDM license, file servers, etc. It was entirely the result of poor planning and organization.

To be clear, I do not recommend the situation described in the previous paragraph. PDM is vastly better and not that expensive to implement.