Jim,
These string operations are part of Core JavaScript, not Acrobat. To learn about using string in the JavaScript language you should take a look at a JavaScript Language Reference. The O'Reilly book is the best but there are plenty of online resources as well.
>>TextField1.rawValue = str1.substr, (6,2)+ str2.substr, (9,2)
This line has a syntax problem, it should be
TextField1.rawValue = str1.substr(6,2)+ str2.substr(9,2);
To keep it from adding the numbers you can force the this expression into a string context like this
TextField1.rawValue = String(str1.substr(6,2))+ String(str2.substr(9,2));
OR
TextField1.rawValue = str1.substr(6,2).concat(str2.substr(9,2));
Thom Parker
WindJack Solutions
www.windjack.com