'opening an existing word document and appending text to it [at the beginning](tried with word 2007)
set word = createobject("word.application")
word.visible=true
Word.Documents.Open "C:\Documents and Settings\sachin\My Documents\abc.docx"
Set objectSelection = Word.Selection
objectSelection.TypeText "This is sample text"
objectSelection.TypeParagraph()
Also See:
Opening a new word document
Opening an existing word document
Opening a new word document and writing text to it
Opening an existing word document and appending text to it at the end.
Saving a new word file
Saving an existing word file
Writing formatted text to a word file
Formatting all content, formatting specific paragraphs or finding and formatting specific text in a word document
Inserting images/pictures to a word file
Creating table in a word document, adding text to cells, adding rows to table
Printing a word file