Multiple preview in Filter Plugin

I'm not sure if this will help you, but you can loop through all openend documents, as shown in the getter example and retrieve the document ids (code below).

// we are ignoring errors so this will not give an invalid error
// message when there are no documents open
//Get actives doc ID:
PIUGetInfo(classDocument, keyDocumentID, &currentDocumentID, NULL);

//Get Number of openend docs:
PIUGetInfo(classApplication, keyNumberOfDocuments, &numDocuments, NULL);

if (numDocuments > 0)
{
for (docCounter = 1; docCounter <= numDocuments; docCounter++)
{
// this routine will error if we select the document

// that is already selected, we don't care about this

// as an error, keep chugging

(void) PIUSelectByIndex(classDocument, docCounter);
GetPathInfo(logfilename);
GetHistoryInfo(logfilename);
}
// this routine will error if we select the document
// that is already selected, we don't care about this
// as an error, keep chugging
//select the original front doc again
(void) PIUSelectByID(classDocument, currentDocumentID);
}