Dont know any app that does it, but here's some info.
The shd file should contain just the print job settings, so you may ignore it.
The spl file contains your print data. It can be recorded in RAW (printer format) or EMF format, dont know what you have.
If its RAW:
It may be in PS or PCL or any other printer standard format. These two are more common. If its PS (file contents usually starts with a % followed by some comments). You should be able to find some ps to pdf converters. Adobe distiller does it. If it's PCL or some other raw format, & if you are a C/C++ developer and can play with the Win32 API, you may open a printer & push the raw data & try to get the print (could use a virtual pdf printer). I'll let you know what functions to use in the API if you want to.
If its EMF:
That's nasty. I dont think its compatible with the standard windows EMF format & it's messy inside. Check this viewer
http://www.codeproject.com/KB/printing/EMFSpoolViewer.aspx[
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I also found this shareware which claims to view spl files of many internal formats
http://www.prnwatch.com/pviewer.htm[
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They might print back