Here's a very simplified example, however, I believe you have to have an iFilter installed for the associated file type before the extractor will work.

Be sure to add a reference to Laserfiche.DocumentServices

// initialize extractor
using(TextExtractor te = TextExtractor.LoadExtractor()){
    // get the document info object
    DocumentInfo doc = (DocumentInfo)this.BoundEntryInfo;
    
    // extract the text
    te.ExtractFrom(doc);
    
    // release the document info objecct
    doc.Dispose();
}

Note that when testing a script in the script editor, it runs on whatever PC you're working on, but when you run it in a workflow it runs server side so you'll need the iFilter in both places.