invocableApex.java

@InvocableApex
public void processEmailWithAttachment(){


//Attachement Part
                List<Messaging.Emailfileattachment> fileAttachments = new List<Messaging.Emailfileattachment>();
                Map<Id,ContentDocumentLink> mapContDocuLink = new Map<Id,ContentDocumentLink>([Select Id, ContentDocumentId FROM 
                                                                                               ContentDocumentLink 
                                                                                               WHERE LinkedEntityId=:oppDetails.Id ]);
                
                Set<Id> setContDocumentId =new Set<Id>();
                
                for (ContentDocumentLink docLinks :mapContDocuLink.values()) { 
                    setContDocumentId.add(docLinks.ContentDocumentId);
                }
                if(!setContDocumentId.isEmpty()){
                    Map<Id,ContentDocument> mapContDocument= new Map<Id,ContentDocument>([Select Id, FileType, Title, FileExtension FROM ContentDocument
                                                                                          WHERE Id IN :setContDocumentId]);
                    Map<Id,ContentVersion> mapContVersion = new Map<Id,ContentVersion>([Select Id,ContentDocumentId, VersionData FROM ContentVersion 
                                                                                        WHERE ContentDocumentId  IN :setContDocumentId]);
                    Map<Id,ContentVersion> mapContVerWithContDocId = new Map<Id,ContentVersion>();
                    if(!mapContVersion.isEmpty()){
                        for (ContentVersion contVerRec :mapContVersion.values()) { 
                            mapContVerWithContDocId.put(contVerRec.ContentDocumentId,contVerRec);
                        }
                    }
                    if(!mapContVerWithContDocId.isEmpty() && (!mapContDocument.isEmpty())){
                        for (Id contDocumentId : setContDocumentId) {
                            
                            Messaging.Emailfileattachment efa = new Messaging.Emailfileattachment();
                            
                            String fileName = mapContDocument.get(contDocumentId).Title.Trim() + '.' + mapContDocument.get(contDocumentId).FileExtension.Trim();
                            efa.setFileName(fileName); //Title of the PDF
                            efa.setBody(mapContVerWithContDocId.get(contDocumentId).VersionData); //Body of the PDF,need to do transfer into blob
                            fileAttachments.add(efa);
                        }
                    }
                }
                
                if(fileAttachments.size()>0){
                    mail.setFileAttachments(fileAttachments);
                }
                mails.add(mail);
                List<Messaging.SendEmailResult> results= Messaging.sendEmail(mails);

}