The issue is that multiple commandline arguments are separated by spaces so, if your file path contains spaces, it will be interpreted as multiple arguments. The way to force a string containing spaces to be interpreted as a single argument is to wrap it in double-quotes. That's how you do it in a console window so that's how you do it in code too:
vb.net Code:
Process.Start("winword", $"""{FilePathtxt.Text}""")
Note that that code uses string interpolation. It is equivalent to:
vb.net Code:
Process.Start("winword", String.Format("""{0}""", FilePathtxt.Text))
or:
vb.net Code:
Process.Start("winword", """" & FilePathtxt.Text & """")
or:
vb.net Code:
Process.Start("winword", ControlChars.Quote & FilePathtxt.Text & ControlChars.Quote)