This is my below code  on insertion of lead record community guest user unable to open pdf attchment although from backend when i am passing lead id its working fine --
public static void sendEmail(Id leadId,String leadStatus){
        List<Messaging.SingleEmailMessage> emailList = new List<Messaging.SingleEmailMessage>();
        EmailTemplate emailTemp = new EmailTemplate();
        String emailTempDevName;
        if(leadStatus == System.Label.PartExp_LeadStatusOpen){
            emailTempDevName= System.Label.PartExp_EmailTempName;
        }else if(leadStatus == System.Label.PartExp_LeadStatusRejected){
            emailTempDevName= System.Label.PartExp_RejectedEmailTempName;
        }
        emailTemp =[Select id, Subject, Body From EmailTemplate Where DeveloperName =:emailTempDevName];
       OrgWideEmailAddress orgWideEmailAddress = [SELECT Id,DisplayName FROM OrgWideEmailAddress WHERE DisplayName =: System.Label.PartExp_OWDForPartnerEmail Limit 1];
       
    Lead leadRecord = [SELECT Id, FirstName, LastName, Email FROM Lead WHERE Id = :leadId  Limit 1];
       // PageReference customPage = Page.PartExp_PrintViewRegistrationForm;
        PageReference customPage = new pagereference('/apex/PartExp_PrintViewRegistrationForm?id='+leadId);
        
        customPage.getParameters().put('id', leadRecord.Id);
        System.debug('leadId:'+leadId);
        
        Blob pdfBlob;
       
        try {
            pdfBlob = customPage.getContentAsPDF();
             System.debug('pdfBlob'+pdfBlob);
        } catch (VisualforceException e) {
             pdfBlob = Blob.valueOf('data');
             System.debug('error dedatil' + e.getStackTraceString());
           System.debug('Error generating PDF: ' + e.getMessage());
          // return;
           }
        
      
         Messaging.EmailFileAttachment attach = new Messaging.EmailFileAttachment();
         attach.setFileName('LeadDetails.pdf');
         attach.setBody(pdfBlob);
         attach.Body = pdfBlob;
         System.debug('attach#'+attach);
         Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
         mail.setTemplateId(emailTemp.Id);
         mail.setTargetObjectId(leadId);
       mail.setOrgWideEmailAddressId(orgWideEmailAddress.Id);
         mail.setFileAttachments(new List<Messaging.EmailFileAttachment>{ attach });
         emailList.add(mail);
        
        if(!emailList.isEmpty()){
            Messaging.sendEmail(emailList);
        }