Sharing Violations from files opened wit

We maintain a large database of PDF (Acrobat files) and share them via an Intranet. We use IIS on NT server4. If a user opens a PDF file with their browser, the file cannot be updated or deleted even by an administrator of the web server. The openresource is not visible from the “Server Manager” as would be a file opened on a network where the drives are shared from the server and mapped by a client. The message “There has been a sharing violation. The source or destination file may be in use” occurs. Is there a way to close the file handles on files opened with the web browser?

Thank You