app.findGrepPreferences = NothingEnum.nothing; 
app.findGrepPreferences.findWhat= ".jpg"; 
app.changeGrepPreferences = NothingEnum.nothing; 
app.changeGrepPreferences.changeTo= ""; 
app.activeDocument.changeGrep(); 
 
app.findGrepPreferences = NothingEnum.nothing; 
app.findGrepPreferences.findWhat= ".JPG"; 
app.changeGrepPreferences = NothingEnum.nothing; 
app.changeGrepPreferences.changeTo= ""; 
app.activeDocument.changeGrep(); 
 
app.findGrepPreferences = NothingEnum.nothing; 
app.findGrepPreferences.findWhat= ".PDF"; 
app.changeGrepPreferences = NothingEnum.nothing; 
app.changeGrepPreferences.changeTo= ""; 
app.activeDocument.changeGrep(); 

app.findGrepPreferences = NothingEnum.nothing;  
app.findGrepPreferences.findWhat= "\.(JPG|jpg|PDF|pdf)\>";  
app.changeGrepPreferences = NothingEnum.nothing;  
app.changeGrepPreferences.changeTo= "";  
app.activeDocument.changeGrep(); 

app.findGrepPreferences.findWhat= "\\.(JPG|jpg|PDF|pdf)\\>"