@wogus1919 Please try specifying AutoFitBehavior.FIXED_COLUMN_WIDTHS
:
Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
builder.startTable();
defectAddRowCell(builder, "header", builder.getPageSetup(), 0);
for(int i=0; i< 20; i++)
defectAddRowCell(builder, "", builder.getPageSetup(), 0);
Table table = builder.endTable();
table.autoFit(AutoFitBehavior.FIXED_COLUMN_WIDTHS);
doc.save("C:\\Temp\\out.docx");