PDFTron SDK supports printing. The library handles all the hard work, you simply have to tell it to show the system print dialog with a document. This can be done with Print.startPrintJob.

Here is how:

void handlePrintJob(Activity activity, boolean isRtl,
    boolean printDocument,
    boolean printDocumentWithAnnotations,
    boolean printDocumentWithAnnotationSummary) {
    int printContent = 0;
    if (printDocument) {
        printContent |= Print.PRINT_CONTENT_DOCUMENT_BIT;
    }
    if (printDocumentWithAnnotations) {
        printContent |= Print.PRINT_CONTENT_ANNOTATION_BIT;
    }
    if (printDocumentWithAnnotationSummary) {
        printContent |= Print.PRINT_CONTENT_SUMMARY_BIT;
    }
    Print.startPrintJob(activity, activity.getString(R.string.app_name), mPdfDoc, printContent, isRtl);
}