react backend and frontend download file

import {  View as ViewFile} from '@/api/SafetyRule';

const Handler_DownLoadFile = (Id:number,IsEnglish:boolean)=>{
    sfParam.Id=Id;
    sfParam.IsEnglish=IsEnglish;
    setSFParam(sfParam);
    console.log(JSON.stringify(sfParam))
    ViewFile(sfParam as SafetyRuleParamPO)
    .then((res)=>{
      if (res.StatusCode == 200 && res.Data){
        if(res.Data.FileContent!=undefined){
          const blob = UtilFile.ConvertBase64UrlToBlob(res.Data.FileContent);
          const url = window.URL.createObjectURL(
            new Blob([blob],{type:'application/pdf'})
          );
          const link = document.createElement('a');
          link.href = url;
          link.setAttribute(
            'download',
            "FileName.pdf",
          );
          // Append to html link element page
          document.body.appendChild(link);
          // Start download
          link.click();
           window.URL.revokeObjectURL(url);
        }
      }else{
        alert("error")
      }
    })
  }

export function  ConvertBase64UrlToBlob(base64Data):Blob {
    const byteCharacters = atob(base64Data);
    const byteNumbers = new Array(byteCharacters.length);
    for (let i = 0; i < byteCharacters.length; i++) {
      byteNumbers[i] = byteCharacters.charCodeAt(i);
    }
    const byteArray = new Uint8Array(byteNumbers);
    const blob = new Blob([byteArray], {type: 'application/pdf'});
    return blob;
  }

import Request from '@/api/request';
import ApiResponsePO from "@/model/ResponseDTO/ApiResponseDTO";

import SafetyRuleViewPO from '@/model/PO/SafetyRuleViewPO'

const http = new Request();

export const urlViewFile = '/api/SafetyRule/View​'

export const View = (params: SafetyRuleParamPO): Promise<ApiResponsePO<SafetyRuleViewPO>> => {
  return http.get<object, ApiResponsePO<SafetyRuleViewPO>>(urlViewFile,params);
}

recommen a :base64 to blob Code Example (codegrepper.com)

backend

        public SafetyRuleViewVO ReadFile(int Id,bool IsEnglish) {
            var safetyVO = GetById(Id);
            var viewVO = new SafetyRuleViewVO();
            if (safetyVO != null) {
                string filePath = IsEnglish ? safetyVO.EnglishVersionFileSharePointPath : safetyVO.ChineseVersionFileSharePointPath;
                byte[] fileContent = File.ReadAllBytes(filePath);
                viewVO = new SafetyRuleViewVO {
                    FileContent = fileContent
                };
            }
            return viewVO;
        }

 public class SafetyRuleViewVO {
        public byte[] FileContent { get; set; }
  }