To run Interop libraries on windows service needs much access permission I guess, windows services should running under system privilege and then it should access your word documents.
To give access create a folder named Desktop in following folders
- for x64 system is necessary to create the following folder:
C:\Windows\SysWOW64\config\systemprofile\Desktop
- for x86 system:
C:\Windows\System32\config\systemprofile\Desktop
(it looks a funny solution but works)
see below snippet
Hot Malva tech blog: How to use Office 2007 Automation in Windows 2008 service[
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OR
Other alternative is to create a console application and use a teak scheduler to run your console application on specific time.
I have used above technique on interop application in console app and it works great with windows scheduler
(Note: the user used to create a windows scheduler should have administrative rights)
Hope it helps