Updated the code and am getting this error:

"Method does not exist or incorrect signature: void add(Messaging.EmailFileAttachment) from the type List<Id> (98:36)"
 

// Mario E.
// Sends Case information to the Interpreting Department
// Email addresses are listed under Custom Labels: custom_VIEmailAddresses

public class custom_VICasesForwarding 
{

    @InvocableMethod(Label='forwardToInterpretingDept')
    public static void forwardToInterpretingDept(List<ID> caseRecords)
    {
        Set<Id> createEmailAddresses = new Set<Id>();

        List<Case> caseList = [select Id, 
                                    Subject, 
                                    CaseNumber, 
                                    Case_Reason__c, 
                                    Case_Issue__c, 
                                    Description, 
                                    Date_Time_of_Call__c, 
                                    VINumber__c, 
                                    Customer_s_VP__c, 
                                    Outbound_Audio__c,
                                    Case_Thread_ID__c,
                              (select Id from EmailMessages)
                              from Case where Id IN :caseRecords];

        for(Case c: caseList)
        {
            // Get Org Wide Email Address and then set it as Reply To address
            OrgWideEmailAddress[] owea = [select Id from OrgWideEmailAddress where Address = 'younameit@emailcompany.com'];
            // Define the email
            Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
            if ( owea.size() > 0 ) 
            {
                email.setOrgWideEmailAddressId(owea.get(0).Id);
            }

            // Sets the TO addresses
            String[] toaddr = new String[System.Label.custom_VIEmailAddresses.split(',')];
            string[] ccaddr = new string[]{};

            // Pulls field data from Case to include in the email body
            email.setSubject('FW: ' + c.CaseNumber + ' : ' + c.Case_Reason__c);
            email.setHtmlBody('Case Number: ' + c.CaseNumber
                                + '<br/>' + 
                                'Case Reason: ' + c.Case_Reason__c 
                                + '<br/>' +
                                'Case Issue: ' + c.Case_Issue__c 
                                + '<br/>' + 
                                + '<br/>' +
                                'Date/Time: ' + c.Date_Time_of_Call__c 
                                + '<br/>' + 
                                'VI #: ' + c.VINumber__c
                                + '<br/>' +
                                'Customer\'s VP #: ' + c.Customer_s_VP__c
                                + '<br/>' +
                                'Outbound Audio #: ' + c.Outbound_Audio__c
                                + '<br/>' +
                                + '<br/>' +
                                + '<br/>' +
                                'Case Description: ' + c.Description 
                                + '<br/>' +
                                + '<br/>' +
                                + '<br/>' +
                                '<i>' + '*Note: If there are any null values, this means this information was not provided by the Case Owner prior to this submission.' + '</i>'
                                + '<br/>' +
                                + '<br/>' +
                                + '<br/>' +
                                '<span style="color: #cccccc;">' + c.Case_Thread_ID__c + '</span>'
                                + '<br/>' +
                                + '<br/>');

            email.setToAddresses(toaddr);

            // Get Attachments
            List<id> ContentDocumentIds = new List<id>();
            for(ContentDocumentLink CDLink : [SELECT
                                                ContentDocumentId,
                                                LinkedEntityId
                                                FROM ContentDocumentLink
                                                WHERE LinkedEntityId=:c.id])
            {
                ContentDocumentIds.add(CDLink.ContentDocumentId);
            }
            for(ContentVersion cVersion : [SELECT
                                            Title,
                                            PathOnClient,
                                            FileType,
                                            VersionData
                                            FROM ContentVersion
                                            WHERE ContentDocumentId IN : ContentDocumentIds])
            {
                blob attachBody = cVersion.versiondata;
                system.debug('attachBody : '+attachbody+'---'+cVersion.Title+'    ||TEST.DEBUG||');
                Messaging.EmailFileAttachment efa = new Messaging.EmailFileAttachment();
                efa.SetFileName(c.CaseNumber+'-'+cVersion.Title+'.'+cVersion.FileType);
                efa.setBody(attachBody);
                ContentDocumentIds.add(efa);
            }

            email.setEntityAttachments(ContentDocumentIds);

            Messaging.sendEmail(new Messaging.SingleEmailMessage[] { email });  
        }
    }  
}