public class sendAnEmail
{
    @InvocableMethod(label='Test' description='sends an email')
    public static void sendEmailWithAttachment(List<id> listofQuoteHeader)
    {   
        Map<Id, Application__c> quotesMap =  new Map<Id, Application__c>([SELECT id,Contact__r.Email FROM Application__c WHERE Id IN :listofQuoteHeader]);
           for(Id QuoteHeaderid :listofQuoteHeader)
           {
               PageReference pref= page.PDFGEN;
               pref.getParameters().put('id',(Id)QuoteHeaderid);
               pref.setRedirect(true);
               
               Attachment attachment = new Attachment();      
               Blob b=pref.getContentAsPDF();
               attachment.Body = b;
               attachment.Name = Datetime.now().format('yyyy-MM-dd HH:mm') + ' ' + 'Quote' + '.pdf';
               attachment.IsPrivate = false;
               attachment.ParentId = QuoteHeaderid;
               attachment.Name='Sign.png';
               insert attachment;
               
               Messaging.SingleEmailMessage semail= new Messaging.SingleEmailMessage();
               Messaging.EmailFileAttachment attach= new Messaging.EmailFileAttachment();
               attach.setFileName('AttachmentEmailFile.pdf');
               attach.setBody(b);
               semail.setSubject('Quote Issued');
            //    String[] emailIds= new String[]{'abc@gmail.com'}; 
            String[] emailIds= new String[]{quotesMap.get(QuoteHeaderid)?.Contact__r.Email};
               semail.setToAddresses(emailIds);
               
               semail.setPlainTextBody('Please find the attached quote details');
               semail.setFileAttachments(new Messaging.EmailFileAttachment[]{attach});
               Messaging.sendEmail(new Messaging.SingleEmailMessage[]{semail});
           }
       
            }
  }

<apex:page standardController="Application__c" renderAs="pdf">
 <h1>
     Application__c.Contact__r.Name
    </h1>
</apex:page>