Decrypting a PGP file in UNIX using java

I have a file "Sample.DAT.txt" which is decrypted by PGP.
Inwindows by replacing the ".txt" extension with ".com"  which when double  clicked opens the "PGP Self Decrypting Archive - Enter passphrase" window,
where i enter the passphrase and click OK creates a "Sample.DAT" . This file when appended with the ".txt"
extension gives me the required decrypted file.


I'm using JAVA running in Window's to execute all this with the below code.

            String cmd = FileToBeDecrypted; // ".com" file which has to be decrypted
            Runtime run = Runtime.getRuntime();
            Process pr = run.exec(cmd);
            
            
            Robot robot = new Robot();  
            robot.delay(5000);
              
                  robot.keyPress(KeyEvent.VK_SHIFT);
            robot.keyPress(KeyEvent.VK_TAB);

            robot.keyRelease(KeyEvent.VK_SHIFT);
            robot.keyRelease(KeyEvent.VK_TAB);

            robot.keyPress(KeyEvent.VK_SHIFT);
            robot.keyPress(KeyEvent.VK_TAB);

            robot.keyRelease(KeyEvent.VK_SHIFT);
            robot.keyRelease(KeyEvent.VK_TAB);
            
            //KeyPress and KeyRelease events for specifying the detination path

            robot.keyPress(KeyEvent.VK_TAB);

            robot.keyRelease(KeyEvent.VK_TAB);

            robot.keyPress(KeyEvent.VK_TAB);

            robot.keyRelease(KeyEvent.VK_TAB);

            //KeyPress and KeyRelease events for specifying the passphrase
 
                  robot.keyPress(KeyEvent.VK_TAB);
            robot.keyRelease(KeyEvent.VK_TAB);
            robot.keyPress(KeyEvent.VK_ENTER);
            robot.keyRelease(KeyEvent.VK_ENTER);                              
            robot.delay(5000);


And now we are in the position to move the logic from Window's based JAVA to UNIX based Java ...
I'm using the below code to replicate the same action.

            sExe = "pgp"
                       + " --decrypt "
                       + " "
                       + inputfile                  
                       + " --symmetric-passphrase "
                       + "passphrase"
                       + " --output "
                       + outputFile;
            Runtime run = Runtime.getRuntime();
            Process pr = run.exec(sExe);
      
            //inputfile---> "Sample.DAT.pgp" (Replacing ".txt" with ".pgp" from the original encrypted file "Sample.DAT.txt")
            //outputfile---> "Sample.DAT"

But it throws some error's,

      java.io.IOException: java.io.IOException: pgp: not found

while running the code

Pelase let me know how to decrypt the file in UNIX based Java?