private InputStream convertPdf(MultipartFile multipartFile) throws IOException {
Assert.notNull(multipartFile, "MultipartFile 为 null");
File file = new File(Objects.requireNonNull(multipartFile.getOriginalFilename()));
FileUtils.copyInputStreamToFile(multipartFile.getInputStream(), file);
FileSystemResource resource = new FileSystemResource(file);
MultiValueMap<String, Object> params = new LinkedMultiValueMap();
params.add("file", resource);
params.add("dstFormat", "pdf");
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<Resource> entity = restTemplate.postForEntity(convertPdfUrl, params, Resource.class);
InputStream ins = Objects.requireNonNull(entity.getBody()).getInputStream();
return ins;
}