Send pdfContent using Trigger in salesforce

Requirement: I have VF page on render as pdf means it is PDF file. I want to send this
pdf when in my object there is field "isSend" checkbox type is equal to true then send to users email ids ,  
Send PDF using trigger using Web Service Class.
you need to create two class and one trigger. And your VF Page Pdf class and page.

Step 1: Create GETPDFContentController Class 
/*
  Before this you need to create a VFPage
*/

/**
*   Created By### refernce No:20180555  :   Sumit Shukla
*   Description :   This Apex class based on REST API which exposes POST method to send Email with
* pdf content
*/


@RestResource(urlMapping='/sendPDFEmail/*')
global class GETPDFContentController{
     @HttpPost
    global static void sendEmail(String EmailIds, String Subject, String body, string recordID) {

    List<String> EmailIds = EmailIds.split(',');

       PageReference ref = new PageReference('/apex/VFPageName?id='+recordID); // Firstly you need to create a VF page render as pdf and Passing the record id in url
        Blob b = ref.getContentAsPDF();

        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();

        Messaging.EmailFileAttachment efa1 = new Messaging.EmailFileAttachment();
        efa1.setFileName('PdfName.pdf');
        efa1.setBody(b);

        String addresses;
        email.setSubject(Subject);
        email.setToAddresses( EmailIds);
        //email.setPlainTextBody(Body);
        email.setHtmlBody(body);
        email.setFileAttachments(new Messaging.EmailFileAttachment[] {efa1});
        Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});

    }
}

Step 2: Create SendVFAsAttachmentController Class 
/**
*   Created By### refernce No:20180556  :   Sumit Shukla
*   Description :   This class exposes @future method to send VF page rendered as PDF as attachment in Email
*/
public class SendVFAsAttachmentController{

    @future(callout=true)
    public static void sendVF(String EmailIds, String Subject,String body, string recordID, String userSessionId)
    {
        //Replace below URL with your Salesforce instance host
       
// Add URL in address and also add in Remote site Setting
// for sandBox and production it will be differnet . SO add url in custom label

            // String url = Label.SendEmailURL; // SendEmailURL is Custom label the is URL is written

            String addr = 'https://cs6.salesforce.com/services/apexrest/sendPDFEmail'; // https://cs6.salesforce.com/ sandBox Url or Prod/dev Url
           // String addr = url;
            HttpRequest req = new HttpRequest();
            req.setEndpoint( addr );
            req.setMethod('POST');
            req.setHeader('Authorization', 'OAuth ' + userSessionId);
            req.setHeader('Content-Type','application/json');
    
            Map<String,string> postBody = new Map<String,string>();
            postBody.put('EmailIds',EmailIds);
            postBody.put('Subject',Subject);
            postBody.put('body',body);
            postBody.put('recordID',recordID);
            String reqBody = JSON.serialize(postBody);
    
            req.setBody(reqBody);
            Http http = new Http();
            HttpResponse response = http.send(req);
        
    }
}

Step 3: Create Trigger on Object
/**
*   Created By### refernce No:20180556  :   Sumit Shukla
*   Description :   This trigger has the condition on that u want to send pdf
*/
  Now Write the Trigger on which object you want to send the Pdf connect


        string strid;
// write the condition as you required
        if(trigger.isAfter && trigger.isUpdate)
        {
             string body ='';
            for(Sobject obj : trigger.new)
            {
  if(isSend ==true)
                strid = obj.id;  
            }
            
              body = 'Dear Sir/Madam, <br/><br/>';
              body += 'Greetings!! <br/> <br/>';
              body += 'Thanks for your order.<br/> <br/>';
              body += 'Thank You<br/>';
              body += 'Regards<br/>';
              body += 'Sumit Shukla';         
         
              SendVFAsAttachmentController.sendVF('Sumitshukla.mca@gmail.com,sumit@gmail.com,shukla@gmail.com',' Subject Name', body, strid , UserInfo.getSessionId());
             
            }
        }
       
      
}