I'm getting the error "Command txs:///view-pdf-external not defined" when I click on the external viewer. Any help please?
Assuming the underlying OS is Windows:
Download and install SumatraPDF from https://www.sumatrapdfreader.org/download-free-pdf-viewer.html (last accessed 2019-08-12-2255UTC+2)
Open TeXstudio and go to
Options -> Configure TeXstudio -> Commands -> External PDF viewerand add the following:
"C:/Program Files/SumatraPDF/SumatraPDF.exe" %.pdf(default path to SumatraPDF, if default install path hasn't been changed during installation process.)
Restart TeXstudio, compile
.texfile, open PDF in external viewer.