"File not found" error when you try to open an Office file from a UNC share

Symptoms

Assume that you enable the Open From universal naming convention (UNC) feature in Microsoft Office Web Apps Server or Office Online Server. When you try to open an Office file from a UNC share by using Office Online, you receive the following error message:

File not found
The URL of the original file is not valid or the document is not publically assessable. Verify the URL is correct, then contact the document owner

Resolution

To resolve this issue, follow these steps:

1. Make sure that the Office file does not exceed 10 MB. 10 MB is the size limit for files that you can open from the UNC share.
2. Grant the computer account of the Office Online server read access to the Sharing permissions. Additionally, grant the computer account read and execute access for the Security permissions. To do this, follow these steps:
   1. Right-click the folder that contains the Office file and then click Properties.
   2. On the Sharing tab, click Advanced Sharing, and then click Permission.
   3. Click Add, click Object Type, click the Computers check box, and then click OK.
   4. In the Enter the object name to select box, type the computer account of the Office Online server (for example, type domain\OfficeServer). Then, click Check Names, and then click OK.
   5. Grant the Read permission to the computer account of the Office Online server that you added, and then click OK.
   6. On the Security tab, click Add, click Object Type, select the Computers check box, and then click OK.
   7. In the Enter the object name to select box, type the computer account of the Office Online server, click Check Names, and then click OK.
   8. Grant the Read & execute permission to the computer account of the Office Online server that you added, and then click OK.