return Rendered page via Apex PageReference

sf-rendarPage-sample

// 現在のsentences データから Solution の Answer を更新
  public PageReference renderContent() {

    PageReference pageRef = new PageReference('/apex/faqpreview?sid=' + solution.id);
    Blob content = pageRef.getContent();
    Solution solution = [SELECT id, Answer__c FROM Solution
      WHERE id = :ApexPages.currentPage().getParameters().get('id')];
    solution.Answer__c = content.toString();
    update solution;

    return ApexPages.currentPage();
  }