Given it's a bad idea to use the Office Automation API on a server anyway, don't worry about not having Office installed. Source: http://support.microsoft.com/kb/257757/en-us
If your documents are all the new Office Open XML (OOXML, .docx
etc) format then you can open them as a *.zip
file and modify the XML that defines the Document bookmarks. See here for more information: http://msdn.microsoft.com/en-us/library/office/bb448854(v=office.15).aspx Warning: the Office Open XML library is very bare-bones, so I hope you're billing by the hour.
The only other option (besides doing everything yourself, which you really don't want to do) is to use a third-party library and so far the only one I can recommend is Aspose ( http://www.aspose.com/ ), but it's expensive.
Disclaimer: I am a Microsoft employee, however this personal recommendation is from my own experience. I do not work on Office.