If you are talking about the PCAD 4.51 version, then you have to first convert then in pdf format. But problem is using that version, i.e. run pcad4.51 and convert it. This pdf is not that Acrobat reader type file, it has same extension.
You need to use PDIFOUT.exe to convert the file to PDIF format. You then will have to read it into a Windows version of PCAD (Accel, or PCAD), and save it to that newer format. Once you've done that, you can use the free PCAD viewer that can be downloaded from the web.
If you have trouble with the conversion, or you don't know how to do the above, you can zip or rar your file and PM it to me. I'll be happy to either convert it to a newer PCAD format for you, or put it in printable format so you can view and print it.