code: private String getHtmlForPDFConversion() throws IOException {
          StringBuilder oldContent = new StringBuilder();
  
          FileReader fr = new FileReader(file);
          try (BufferedReader reader = new BufferedReader(fr)) {
              String line;
              while ((line = reader.readLine()) != null) {
                  oldContent.append(line);
                  oldContent.append("\r\n");
              }
          }
  
          // replace all non convertible elements with empty text or modify for conversion
          String str = oldContent.toString()
                  .replaceAll("<script type='text/javascript'>(?s).*</script>", "")
                  .replaceAll("<tr>\\s*<th>View Results</th>(?s).*?</tr>", "")
                  .replaceAll("&nbsp;", " ");
  
          String imagePattern = "(<img(?s).*? src='(.*?)'(?s).*?)</img>";
          Pattern r = Pattern.compile(imagePattern);
          Matcher m = r.matcher(str);
          int imageCount = 0;
          while (m.find()) {
              str = str.replaceFirst("<a href='javascript:void\\(0\\)'(?s).*?(<img(?s).*? src='(.*?)'(?s).*?)" +
                              " style(?s).*?</img>",
                      "<a href=\"#image-" + imageCount + "\">View Screenshot</a>");
              str = str.replaceFirst("</body>", "<p style='page-break-before: always' id='image-" + imageCount++ + "'></p" +
                      ">" +
                      m.group().replaceAll("width='300px' style(?s).*?'>", "height='600px' width='1000px'>") + "</body>");
          }
          return str;
      }
docs: Removes all elements that cannot be converted to pdf, this method is to be used
  before converting the html file to pdf with openhtmltopdf.pdfboxout.PdfRendererBuilder