There are some similarities between Word and Excel, but they are not the same when it comes to programming. If you Add a document without reference to the template, which is what you had originally, then a new document is created from the normal template. Essentially a blank document unrelated to your document with the button. If you want to create a new document that has the button then you need to refer to the template e.g.
Set objDoc = Documents.Add(Template:="C:\WordTrial\cmdBtnWord.d ocm")
This will create a new document that is an unnamed facsimile of the original. Or as it is a macro enabled document, you can simply open it as in your subsequent attempt.
Having got the document open/created your code then writes a text value to the document range, which overwrites everything in the document body. You need instead to set a range to the start (or end) of the document and write to that e.g.
Code:
Dim txtword As String
Dim objDoc As Document
Dim objRange As Range
Dim objTable As Table
Dim intRows As Integer
Dim intCols As Integer
txtword = "fsdhfkhfkdhfdskfhd fkdshfdkfhdskfhdsfd fdshgfdjdsjfg" & vbCr
Set objDoc = Documents.Add(Template:=ThisDocument.FullName)
Set objRange = objDoc.Range
objRange.Collapse Direction:=wdCollapseStart
objRange.Text = txtword
objRange.Collapse Direction:=wdCollapseEnd
intRows = 8: intCols = 5
Set objTable = objDoc.Tables.Add(objRange, intRows, intCols)
objTable.Borders.Enable = True
AutoNew and AutoOpen are built-in macro names that run when the document is opened or created and go in a standard module. They perform similar roles to Document_New and Document_Open
You would need to modify the ribbon in order to add a button there. See
Customize the Office Ribbon (It doesn't take rocket science)