API query to retrieve document from product/folder

You could implement something similar to https://community.ptc.com/t5/Windchill-Questions/Download-representation-and-annotation-of-a-WTDocument-in/td-p/150204

You would just need to modify to search for a WTDocument versus EPMDocument and add your additional where clauses.  Also, you would need to access the primary versus the secondary content with something similar to the code below.

public static void downloadFile (ApplicationData appData, String dlLoc, String fileName) 
{
	System.out.println("start download file()");
	System.out.println("==========");
	try { 
 	File file = new File(dlLoc +"\\"+ fileName);
 	System.out.println("temp path: "+ file);
 	String filePath = file.getCanonicalPath();
 	InputStream istream =ContentServerHelper.service.findContentStream(appData);
 	OutputStream ostream = new FileOutputStream(filePath);
 	ContentServerHelper.service.writeContentStream(appData,filePath);
 	istream.close();
 	ostream.close();
 	System.out.println("end downloadFile");
	}
 catch (Exception e)
 {
 System.out.println("Exception occured,downloadFile"+ e);
 }
}
	
public static ApplicationData findPrimary(EPMDocument EPMDoc) throws WTException, PropertyVetoException 
{
	System.out.println("Starting findPrimary");
	System.out.println("==========");
	ApplicationData primaryNotFound = null;
	FormatContentHolder documentWithContents= (EPMDocument) ContentHelper.service.getContents(EPMDoc);
	@SuppressWarnings("unchecked")
	Vector<ContentItem> vector=ContentHelper.getContentList(documentWithContents);
	vector.addElement(ContentHelper.getPrimary(documentWithContents));
	for (int i=0; i<vector.size(); i++)
	{
	 if (vector.elementAt(i) instanceof ApplicationData)
	 { 
	 ApplicationData appData = (ApplicationData)vector.elementAt(i);
	 if(appData.getFileName().equals("{$CAD_NAME}")) {
	 System.out.println("found primary content");
	 appData.setFileName(EPMDoc.getCADName());
	 System.out.println("Renamed file: " + appData.getFileName());
	 System.out.println("pass back to createZipList");
	 return appData;
	 }
	}
 }
 return primaryNotFound;
}