In the past some 3rd party programs existed that could have been used to export AutoCAD slide files (.sld) to PDF, or other formats. Unfortunately, most of them seems to be no longer available, which makes sld to pdf conversion somewhat tricky nowadays. The only remaining option would probably be to use AutoCAD or some of its add-ons to handle the Autodesk .sld files.
As for other SLD file types, which are mostly various slideshows. Programs that can view them, can also usually print them which can be used to convert sld to pdf in case you have a virtual PDF printer installed.Open SLD file Open PDF file