如何通过Google脚本将Google驱动器中的PDF转换为文本

Question

我正在研究将Google驱动器中的PDF转换为文本的代码。而且，我可以按以下代码转换PDF。但是，当我尝试通过URL在Google驱动器中指定PDF时（例如var url =“ https://drive.google.com/open?id=1gs-WvPPPPPPP0-iaawwadafa--”;）。该代码不起作用。

var url = "https://www.test.com/sites/g/files/xyz123.pdf";  
    // It works fine.  And, if changes to google drive URL, it doesn't work.  
var blob = UrlFetchApp.fetch(url).getBlob();
    // No error showed up at getBlob.

Logger.log(blob) // shows "Blob" after changes to google drive URL
Logger.log(blob.getName()) // shows "open.html" after changes to google drive URL
Logger.log(blob.getContentType()) // shows "text/html" after changes to google drive URL

var resource = {
    title: blob.getName(),
    mimeType: blob.getContentType()    
};

var file = Drive.Files.insert(resource, blob, {ocr: true, ocrLanguage: "en"});
    // At above line, Error message "OCR is not supported for files of type text/html (line 64, file "Code")" showed. 

var doc = DocumentApp.openById(file.id);
var text = doc.getBody().getText();

return text; 

我想将Google驱动器文件夹中的PDF文件一一转换为TEXT。