Dim outStr As System.IO.MemoryStream = New System.IO.MemoryStream()
The original document stream "documentToMerge" is made of only "Arial Unicode MS" fonts, the output PDF file is showing english text OK. But all Gujarati unicode characters are misarranged. (Probably words split at erratic characters, or adding spaces between characters, or skipping some characters).
Submitting herewith original docx and output PDF for comparison. Please have a look at gujarati text in output file.