How to replace words or characters in Kendo Editor when paste.
How to prevent pasting particular text in Kendo Editor, (Content Block or Long text field)

To achieve this functionality, extending the Sitefinity CMS backend UI is required. The backend interface is powered by the Sitefinity CMS Admin App, which is a Single Page Application (SPA) built using Angular, TypeScript, and OData web services for content management. The Admin App is extensible.

A technical overview of the backend interface and its extensibility options is available here:

https://www.progress.com/documentation/sitefinity-cms/technical-overview-and-extensibility 

For extending the Admin App, refer to the official Sitefinity CMS Admin App Extensions Development Kit, which includes samples and guidance:

https://github.com/Sitefinity/sitefinity-admin-app-extensions

To paste cleanup (replace a text value with the new one), extend the AdminApp editor and use a custom function to manage the text. For example (past-cleanup-provider.ts):

import { ClassProvider, Injectable } from '@angular/core';
import { ToolBarItem, EditorConfigProvider, EDITOR_CONFIG_TOKEN } from '@progress/sitefinity-adminapp-sdk/app/api/v1';

@Injectable()
class PasteCleanupProvider implements EditorConfigProvider {
    getToolBarItems(editorHost: any): ToolBarItem[] {
        return [];
    }

    getToolBarItemsNamesToRemove(): string[] {
        return [];
    }

    configureEditor(configuration: any) {
        configuration.pasteCleanup.custom = html => {
            return html.replace('OldText', 'NewText'); 
            // To disallow pasting images, RegEx can be used, for example:
            // return html.replace(/<img[^>]*>/g, '');
        };

        return configuration;
    }
}

export const PASTE_CLEANUP_PROVIDER: ClassProvider = {
    multi: true,
    provide: EDITOR_CONFIG_TOKEN,
    useClass: PasteCleanupProvider
};

The sample is based on Kendo Editor functionality described here:

• Progress Kendo UI for jQuery Documentation, Editor - Configuration - pasteCleanup https://docs.telerik.com/kendo-ui/api/javascript/ui/editor/configuration/pastecleanup#pastecleanupcustom

More AdminApp extensions (including Kendo Editor) are available here:

• GitGub, Sitefinity/sitefinity-admin-app-extensions-samples/editor-extender https://github.com/Sitefinity/sitefinity-admin-app-extensions-samples/tree/master/editor-extender