PDF (adobe.com)

Accidentally updating your work

In most cases, the update commands are disabled for content you have checked out, because that content would always be up to date. However, an undesirable situation can occur if a different user deletes the lock on checked-out content (by dragging the lock file [.idlk] to the Recycle Bin [Windows] or Trash [Mac OS]), and modifies the content. In this case, the update commands can become enabled even while the content is checked out to you, essentially allowing two people to edit the content at the same time. Updating the content results in lost work. For best results, do not delete the lock files.