sendEmail.cls

public static void sendEmail(Map<Id, Order> orderMap) {
    List<ContentDocumentLink> contentDocumentLinks = [
        SELECT Id, ContentDocumentId, LinkedEntityId
        FROM ContentDocumentLink
        WHERE LinkedEntityId IN :orderMap.keySet()
    ];

    Map<Id, List<ContentDocumentLink>> contentDocumentLinksByOrderId = new Map<Id, List<ContentDocumentLink>>();
    Set<Id> contentDocumentIds = new Set<Id>();

    for (ContentDocumentLink contentDocumentLink : contentDocumentLinks) {
        if (contentDocumentLinksByOrderId.containsKey(contentDocumentLink.LinkedEntityId)) {
            List<ContentDocumentLink> tempContentDocumentLinks = contentDocumentLinksByOrderId.get(contentDocumentLink.LinkedEntityId);
            tempContentDocumentLinks.add(contentDocumentLink);
            contentDocumentLinksByOrderId.put(contentDocumentLink.LinkedEntityId, tempContentDocumentLinks);
        } else {
            contentDocumentLinksByOrderId.put(contentDocumentLink.LinkedEntityId, new List<ContentDocumentLink>{ contentDocumentLink });
        }
        contentDocumentIds.add(contentDocumentLink.ContentDocumentId);
    }

    List<ContentVersion> contentVersions = [
        SELECT Id, ContentDocumentId, PathOnClient
        FROM ContentVersion
        WHERE ContentDocumentId IN :contentDocumentIds AND IsLatest = TRUE
    ];

    Map<Id, ContentVersion> contentVersionsByContentDocumentId = new Map<Id, ContentVersion>();
    for (ContentVersion contentVersion : contentVersions) {
        contentVersionsByContentDocumentId.put(contentVersion.ContentDocumentId, contentVersion);
    }

    EmailTemplate emailTemplate = [SELECT Id, Body, Subject FROM EmailTemplate WHERE DeveloperName = 'Demo_Team' LIMIT 1];

    List<Messaging.SingleEmailMessage> emailMessages = new List<Messaging.SingleEmailMessage>();

    for (Order order : orderMap.values()) {
        List<String> entityAttachmentIds = new List<String>();

        List<ContentDocumentLink> orderContentDocumentLinks = contentDocumentLinksByOrderId.get(order.Id);
        if (orderContentDocumentLinks != null && orderContentDocumentLinks.size() > 0) {
            for (ContentDocumentLink contentDocumentLink : orderContentDocumentLinks) {
                ContentVersion contentVersion = contentVersionsByContentDocumentId.get(contentDocumentLink.ContentDocumentId);
                entityAttachmentIds.add(contentVersion.Id);
            }
        }


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

        email.setPlainTextBody(Messaging.renderStoredEmailTemplate(emailTemplate.Id, UserInfo.getUserId(), order.Id).plainTextBody);
        email.setSubject(emailTemplate.Subject);
        email.setToAddresses(new List<String>{ '[email protected]' });

        emailMessages.add(email);
    }

    Messaging.sendEmail(emailMessages);
}