There is only one file type that uses the .LPDF extension:
Localized PDF File
Multilingual .PDF file, often named About Stacks.lpdf and About Downloads.lpdf, and found on Mac OS X systems; and saved in the Mac OS X package format and stores both the .PDF file as well as data that localizes the document for multiple languages.
LPDF files can be opened in Mac OS X with Apple Preview, the built-in previewer for PDF files.
NOTE: LPDF files are not PDF files. They are a specifically-formatted Mac OS X package that contains a PDF file as well as localization information.
About Stacks.lpdf - Located in the users' Documents directory and explains how Document Stacks are used in Mac OS X.
About Downloads.lpdf - Located in the users' Downloads directory and provides information about how Mac OS X manages file downloads.
Updated: February 27, 2013