How to save as .txt in vba

Manually changing the extension of the file name does not actually change the file type. The SaveAs method takes a file type argument. The code you want is

ActiveWorkbook.SaveAs Filename:="e:" & "HDR" + Format(Now(), "YYYYMMDDhhmmss") _
& ".txt", FileFormat:= xlTextWindows

Doing a search from within Excel help for XlFileFormat will get you (almost) the full list of possible file formats, including 6 text formats, and 4 CSV formats.

Adding txt to the name does not automatically encode the word document into plain text format.

Instead attempt

ActiveWorkbook.SaveAs Filename:="e:" & _
"HDR" + Format(Now(), "YYYYMMDDhhmmss") & ".txt", FileFormat:=wdFormatText, Encoding:=1252