JavaScript in general consists of the Core, and application-specific extensions. Web browser client-side JavaScript consists of the Core and webbrowser-client-side-specific extensions. Server-side JavaScript consists of the Core ans server-specific extensions. Acrobat JavaScript consists of the Core and Acrobat/PDF-specific extensions. ActionScript consists of the Core and Flash-specific extensions and so on… So, for scripting in Acrobat/PDF, you have to know about the Core, the Acrobat/PDF-specific extensions, as well as the PDF document object model. IMHO, the best reference about the Core is Flanagan's book "JavaScript, the definitive Guide (now in its 6th edition), published by O'Reilly. The reason why it is my favorite, it makes a clear distinction between Core and (well, probably the most common use) webbrowser-specific extensions. But because the distinction exists, it is easy to ignore the non-Core stuff. And for Acrobat/PDF JavaScript, you will have to get the Acrobat SDK documentation, where you will find the Acrobat JavaScript documentation. Hope this can help.
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