async downloadDocument(documentId) {
    try {
      const document = await PaperlessService.getDocument(documentId);
      const tempFilePath = path.join(this.tempDir, `${documentId}_${document.original_filename}`);
      
      // Create download stream
      const response = await PaperlessService.client.get(`/documents/${documentId}/download/`, {
        responseType: 'stream'
      });

      // Save file temporarily
      await pipeline(
        response.data,
        fs.createWriteStream(tempFilePath)
      );

      return {
        filePath: tempFilePath,
        filename: document.original_filename,
        mimeType: document.mime_type
      };
    } catch (error) {
      console.error(`Error downloading document ${documentId}:`, error);
      throw error;
    }
  }
Downloads the original file from Paperless
@param {string} documentId - The ID of the document
@returns {Promise<{filePath: string, filename: string, mimeType: string}>}