Ttdfjt

Here is my code.

$pdfFile = 'pub/pdf/13_rajeshnagappan2016@gmail.com.pdf';
 $store = $this->_storeManager->getStore()->getId();
 $transport = $this->_transportBuilder->setTemplateIdentifier('enquiry_test_template')
 ->setTemplateOptions(['area' => 'frontend', 'store' => $store])
 ->setTemplateVars(
 [
 'store' => $this->_storeManager->getStore(),
 ]
 )
 ->setFrom('general')
 ->addTo('rajeshnagappan2016@gmail.com', 'Customer Name');
 // ->addAttachment(file_get_contents($pdfFile));

 try 
 $transport = $this->_transportBuilder->getTransport();
 $transport->sendMessage();
 $this->_inlineTranslation->resume();
 catch (Exception $e) 
 echo $e->getMessage(); die;
 

Ensure that you are using the right area code

email_templates.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Email:etc/email_templates.xsd">
 <template id="..." label="This is email template" file="general_template.html" type="html" module="..." area="frontend"/>
</config>

template options

$templateOptions = [
 'area' => Area::AREA_FRONTEND,
 ];

and in that case your controller class should be in the frontend area too

Finally I got solution...

etc/di.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<preference for="MagentoFrameworkMailMessage" type="OfferEnquiryModelMessage" /></config>

Model/Mail/Message.php

<?php 
namespace OfferEnquiryModel;

class Message extends MagentoFrameworkMailMessage 

protected $_parts = [];

public function setBodyText($content) 
 $textPart = new ZendMimePart();
 $textPart->setContent($content)
 ->setType(ZendMimeMime::TYPE_TEXT)
 ->setCharset('utf-8')
 ;
 $this->_parts[] = $textPart;
 $this->setPartsToBody();
 return $this;


public function setBodyHtml($content) 
 $htmlPart = new ZendMimePart();
 $htmlPart->setContent($content)
 ->setType(ZendMimeMime::TYPE_HTML)
 ->setCharset('utf-8')
 ;
 $this->_parts[] = $htmlPart;
 $this->setPartsToBody();
 return $this;


public function createAttachment($content, $fileType, $disposition, $encoding, $fileName) 
 if($content === null) throw new Exception("Param 'content' can not be null");
 if($fileType === null) $fileType = 'application/pdf';
 if($disposition === null) $disposition = ZendMimeMime::DISPOSITION_ATTACHMENT;
 if($encoding === null) $encoding = ZendMimeMime::ENCODING_BASE64;
 if($fileName === null) throw new Exception("Param 'filename' can not be null");
 $attachmentPart = new ZendMimePart();
 $attachmentPart
 ->setContent($content)
 ->setType($fileType)
 ->setDisposition($disposition)
 ->setEncoding($encoding)
 ->setFileName($fileName)
 ;
 $this->_parts[] = $attachmentPart;
 $this->setPartsToBody();
 return $this;


public function setPartsToBody() 
 $mimeMessage = new ZendMimeMessage();
 $mimeMessage->setParts($this->_parts);
 $this->setBody($mimeMessage);
 return $this;

Model/Mail/TransportBuilder.php

<?php
namespace OfferEnquiryModelMail;
class TransportBuilder extends MagentoFrameworkMailTemplateTransportBuilder

/**
* @param ApiAttachmentInterface $attachment
*/
public function addAttachment($pdfString)

 $this->message->createAttachment(
 $pdfString,
 'application/pdf',
 Zend_Mime::DISPOSITION_ATTACHMENT,
 Zend_Mime::ENCODING_BASE64,
 'attatched.pdf'
 );
 return $this;

 public function clearHeader($headerName)

 if (isset($this->_headers[$headerName]))
 unset($this->_headers[$headerName]);
 
 return $this;

Controller/Index.php

$pdfFile = 'pub/'.$fileName;
 $this->inlineTranslation->suspend();
 $transport = $this->_transportBuilder->setTemplateIdentifier('enquiry_test_template')->setTemplateOptions(
 [
 'area' => Area::AREA_FRONTEND,
 'store' => $this->_storeManager->getStore()->getId(),
 ]
 )->setTemplateVars(
 [
 'message' => 'this is test with send mail',
 ]
 )->setFrom(
 [
 'email' => 'rajeshnagappan2017@gmail.com',
 'name' => 'Test'
 ]
 )->addTo(
 'rajeshnagappan2016@gmail.com', 'Receiver'
 )->addAttachment(file_get_contents($pdfFile))->getTransport();
 $transport->sendMessage();
 $this->inlineTranslation->resume();
 $this->sendMail();