请参阅API食谱，在这里下载文档
下面是下载文档的示例代码。

envelopesApi.getDocument(accountId, envelopeId, documentId, function (error, document, response) {
    if (error) {
      console.log('Error: ' + error);
      return;
    }

    if (document) {
      try {
        var fs = require('fs');
        var path = require('path');
        // download the document pdf
        var filename = accountId + '_' + envelopeId + '_' + documentId + '.pdf';
        var tempFile = path.resolve(__dirname, filename);
        fs.writeFile(tempFile, new Buffer(document, 'binary'), function (err) {
          if (err) console.log('Error: ' + err);
        });
        console.log('Document ' + documentId + ' from envelope ' + envelopeId + ' has been downloaded to ' + tempFile);
      } catch (ex) {
        console.log('Exception: ' + ex);
      }
    }
  });

我们今天遇到了同样的问题，这不是因为Docusign API，而是因为我们使用了Amazon Lambda函数;为了让它工作，我们不得不改变一点我们的无服务器。yml文件并添加一个binaryMediaTypes部分，如下所示：

provider:
  name: aws
  runtime: nodejs12.x
  region: eu-west-3
  profile:xxxxx
  versionFunctions: false
  apiGateway:
    binaryMediaTypes:
      - 'text/html'

希望能有所帮助

var https = require（'follow-redirects'）。https; var fs = require（'fs '）;

var options = {
        'method': 'GET',
        'hostname': 'demo.docusign.net',
        'path': '/restapi/v2/accounts/{account_id}/envelopes/{envelope_id}/documents/combined',
        'headers': {
          'X-DocuSign-Authentication': ' {"Username": "*******","Password": "******","IntegratorKey": "*******"}'
        },
        'maxRedirects': 20
      };

      var req = https.request(options, function (res) {
        var chunks = [];

        res.on("data", function (chunk) {
          chunks.push(chunk);
        });

        res.on("end", function (chunk) {
          var body = Buffer.concat(chunks);

          var filename = '_combined.pdf';
        var tempFile = filename;
        fs.writeFile(tempFile, Buffer.from(body,"binary"), function (err) {
          if (err) console.log('Error: ' + err);
        });
        console.log('Document from envelope has been downloaded');

        });

        res.on("error", function (error) {
          console.error(error);
        });
      });

      req.end();

调用envelopesApi时。Docusign Node SDK中的getDocument，返回的数据格式是什么？
eSignature NodeJS SDK的getDocument方法默认返回二进制编码的字符串。或者，您可以请求它返回base64编码的字符串。
如何将其写入文件？
如果它是一个二进制编码的字符串，则需要使用Buffer.from(STRING, 'binary')将其解码为原始二进制缓冲区，然后将结果写入内存。如果它是base64编码的字符串，它是一样的，但您使用'base64'代替。
基于Promise的版本：

const fs = require('fs/promises');
const path = require('path');
const { Buffer } = require('buffer');
const docusign = require('docusign-esign');

async function writeDocument(dsApiClient, { accountId, envelopeId, documentId }) {
  try {
    const envelopesApi = new docusign.EnvelopesApi(dsApiClient);
    const binString = await envelopesApi.getDocument(accountId, envelopeId, documentId);
    const filepath = path.resolve(__dirname, `document_${documentId}`);
    await fs.writeFile(filepath, Buffer.from(binString, 'binary'));
  } catch (error) {
    throw new Error('Unable to write document to disk', { cause: error });
  });
}

你可以这样称呼它：

// Initialize DocuSign Api Client
const dsApiClient = new docusign.ApiClient();
dsApiClient.setBasePath(BASE_PATH);
dsApiClient.addDefaultHeader('Authorization', `Bearer ${ACCESS_TOKEN}`);

(async () => {
  try {
    await writeDocument(dsApiClient, { accountId, envelopeId, documentId });
  } catch(error) {
    console.log('Could not save DocuSign document', error);
  }
});