>I need to set up a program to search documents (MS-Word o.a) for selected words or word combinations. Is there any general tool to index a lot of documents and on select show a abstract or a piece of the text or just open the selected document?

You can use search tools embedded into Office applications. As far as I remember there is a "Find" button on a toolbar and in "Open file" dialog.
A similar tool I have made a few years ago. The main idea was very simple:
1. Scanning selected directories and saving of Word files path and text contents into table using OLE automation (Document.Range.Text property).
2. Searching documents for words in table.
3. Opening document using ShellExecute() API function.
But it was a long ago and I haven't sources now.