Probably because filetype pde does not exist in thetyty.vim file.
Basically, you need to create your own typety.vim file in ~ / .vim / (which will be received before the systemtype.vim file) or add to your .vimrc:
" Arduino files
au BufNewFile,BufRead *.pde setf pde
(On the other hand, gsp already exists in filetype.vim by default, 763
" GNU Server Pages
au BufNewFile,BufRead *.gsp setf gsp " GNU Server Pages
au BufNewFile,BufRead *.gsp setf gsp )
See :help new-filetype for more information on how to implement a new file type.
source share