<p>How do I load MS Word document (.doc and .docx) to memory (variable) without doing this?:</p>

<p><em>wordApp.Documents.Open</em> </p>

<p>I don't want to open MS Word, I just want that text inside. </p>

<p>You gave me answer for DOCX, but what about DOC? I want free and high performance solution - not to open 12.000 instances of Word to process all of them. :( Aspose is commercial product, and 900$ is a way too much for what I do.</p>

If you are dealing with docx you can do this with out doing any interop with Word
.docx file actually a ZIP contains an XML file , you can read the XML 
Please refer the below links
http://conceptdev.blogspot.com/2007/03/open-docx-using-c-to-extract-text-for.html
Office (2007) Open XML File Formats