If you are trying to use XPaths in the PDF there is a an applyXPath method available in the Acrobat API, documented in js_api_reference.pdf which is part of the Acrobat X SDK available at http://www.adobe.com/devnet/acrobat/sdk/eula.html or in the Acrobat 8 version directly at http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/js_api_reference.p...
So if my form had some xml like;
The following will display 1263678 on the console;
console.println(XMLData.applyXPath($data, '//*[@name = "RequestId"]').item(0).value);
That is the value of the first element with a name attribute of RequestId.
I’ve never got this method to work with namespaces and the context is not what I would expect, in this example the root should be $data, but it is still possible to pick up elements from the XFA template. This is one reason why the XPath expressions I used ended up being more complicated than they could have been, like the one above.
So I stick with SOM expression, but for simple relative XPaths you can use the following to convert to a SOM;
// Attempt to turn a relative XPath into a relative SOM expression
// e.g. ../../clientId/text() becomes parent.parent.clientId
xpath = stripNamespacePrefixes(xpath);
xpath = xpath.replace(/\.\.\//g, "parent.");
xpath = xpath.replace(/\/text\(\)/, "");
xpath = xpath.replace(/\//g, ".");
// Strip all namespace prefixes from an xpath expression
// e.g. /default:collections/default:collection/@reportingPeriod
// will become
return xpath.replace(/\/\w*?:/g, "/");
This is far from a general routine but maybe somewhere to start.