Use field placeholders in a Rich Text field

I’m creating Document Templates for a client where they can create a letter and add placeholders for the patient’s name, address, etc., then generate and save the letter.

I’m saving the template content in a Rich Text field. Here is an example:

{field_1463} (this is the patient’s name field from the document table)
{field_1464} (this is the patient’s DOB field from the document table)

Dear {field_1463.First Name},

Thank you for letting us Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

When I view the content in a detail page or html, the fields are not populating. Here is an example of when it’s viewed.

{field_1463}
{field_1464}

Dear {field_1463.First Name},

Thank you for letting us Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Any ideas on how to make this work? Thank you!