C2E1_SimplePdf creates a simple "Quick brown fox jumps over the lazy dog" PDF with some images, but without any structure. This results in a regular PDF.
C2E2_TaggedPdf.java uses the same code as the first example, but now we ask iText to introduce structure. This results in a Tagged PDF.
C2E3_PdfA3b.java adapts the first example, so that it conforms to the PDF/A-3 standard, level B (for Basic). The resulting PDF is not a Tagged PDF.
C2E4_PdfA3a.java adapts the third example, so that it conforms to the PDF/A-3 standard, level A (for Accessibility). The resulting PDF is a Tagged PDF.