public with sharing class PDFWbrController {
    public String tstr { get; set; }
    
    public List<String> getWbrStr() {
        List<String> rtn = new List<String>();
        if (String.isBlank(tstr) == false) {
            for (Integer i = 0; i < tstr.length(); i++) {
                rtn.add(tstr.substring(i, i + 1));
            }
        }
        return rtn;
    }
}