Issue seems to be related to UNC paths. But I'm have no time to check deeply. Consider to do something like this.
;~ #RequireAdmin
;My paths
Local $sFileName="10page.pdf"
Local $sTempDir=@TempDir & "\TempPDFTK\"
Local $sPDFTKPath=@ScriptDir & "\pdftk.exe"
Local $sDirBurst=@ScriptDir & "\Busrt\"
;just for delete all
DirRemove($sDirBurst) ;delete the burst out files path
DirRemove($sTempDir) ;delete the temp folder
;Create Directories
If not FileExists($sTempDir) Then DirCreate($sTempDir)
If not FileExists($sDirBurst) Then DirCreate($sDirBurst)
;build path and run PDFTk.exe
Local $sFileFromPath=@ScriptDir & "\" & $sFileName
Local $sFileToPath=$sTempDir & $sFileName
FileCopy($sFileFromPath,$sFileToPath,1)
Local $iExitCode=RunWait(_quotePath($sPDFTKPath) & " " & _quotePath($sFileToPath) & ' burst',$sTempDir,@SW_SHOW)
FileMove($sTempDir & "*.*",$sDirBurst,1) ;move temp files to my burst directory
DirRemove($sTempDir) ;delete temp folder
Exit
Saludos