the Cell.add(" Cell Content ") does not work in Itext7 version 7.1.12 . is is this from me or from the Itext7 ? here are some codes

Cell SubTitle = new Cell().setBold();
Cell CA1Title = new Cell().setBold().setTextAlignment(TextAlignment.CENTER);
Cell CA2Title = new Cell().setBold().setTextAlignment(TextAlignment.CENTER);
Cell ExamTitle = new Cell().setBold().setTextAlignment(TextAlignment.CENTER);
Cell TotalTitle = new Cell().setBold().setTextAlignment(TextAlignment.CENTER);
Cell RemarkTitle = new Cell().setBold();
SubTitle.add("Subject");
CA1Title.add("1st C.A");
CA2Title.add("2nd C.A");
ExamTitle.add("Exam");
TotalTitle.add("Total Score");
RemarkTitle.add("Remark");

The method Cell.add() doesn't accept argument(String).

What is the problem?

In iText, not all elements can accept just "simple" text - some elements are containers for other "Block" elements, whereas the Text is a Leaf element. Actual text is represented by objects of Text or Paragraph type:

Text text1 = new Text("Text 1");
Paragraph p1 = new Paragraph(text1);
Paragraph p2 = new Paragraph("Text 2");

The Cell itself (as its documentation says) is simply a container that holds other elements (and provides col/row spanning for Tables). So to add text to it you need to give it a Paragraph element to hold onto:

Cell myCell = new Cell()
    .add(new Paragraph("My Cell Title"))
    .setBold()
    .setTextAlignment(TextAlignment.CENTER);