You need to send a PDF file of your AutoCAD/LT DWG file to a recipient not interested in any other format, and your version of LT does not have a built-in PDF driver in the PLOT command or you prefer something better than the one built-in.
All you need is a PDF driver installed in Windows to PLOT to in AutoCAD, as well as the side perk of being able to Print to it from other programs like MSWord or MSExcel etc. to create PDF files too.
Free PDF drivers that work just fine in WindowsXP or higher are available through any internet search like this one, just click HERE.
If you have a problem with free, almost all of the vendors at the above link will sell you more advanced versions with more features and abilities.