Besides using Unlocker, there is another way (Process Explorer) to delete an open file in Windows. Here is my example:
1) The system tells me the Track_3.pdf can not be deleted as it is being used.
2) Launch the Process Explorer then search the file name, then click the search result.
3) Right click the highlighted entry and choose ‘Close Handle’, then ‘Yes’ to accept the warning.
4) Now let me try again.