Drupal 8 app development

I have Case Management software for a process serving business (similar to a courier delivery business) developed using Drupal 8 framework. It captures client details, individual case details such as delivery address and such, delivery notes, times and dates etc. The existing development has been tested and functionality is working fine. Additional functionality is required (although partially completed already) including ability to generate documents from templates (provided by me) by merging in job specific details from the app into such templates: • into template Word or PDF documents • into email templates to be sent automatically or manually from the app or through my Outlook • into my third party MYOB accounting system to generate invoices only (purely field insertion into the accounts invoice template) I need to be able to add or edit templates for all of the above. I can set up each template with the relevant fields within each template provided I have the ID for each field. All templates are to be organised into an easily accessible “library” subdivided into a few sections with the ability for me to select which section/template is to be generated. The templates to be used for each individual “job” will be determined according to the values of one or two combined fields within each job - with the ability to re-select the template manually and also edit the generated document manually. Thereafter the generated template will be downloaded and saved to my own pc/server. The generated documents do not need to be stored on the app itself. I also need some read-ahead enabling for a couple of fields within the existing app fields.