2 choices -
1 - Modify the template so it reads something like Dear Name (Use a word "Name" that does not apear anywhere else in the document.)
Open up the Find/Change dialog (ctrl+f)
Find = Name (or your choice)
Replace = Rob
select Change All
2 - If you have a bulk of such to create, set the names in a excel file. Save as csv. Use Data Merge. If they are single page documents, instruct Data Merge to limit number of records to 1. (If you had 100 (name) records to merge InDesign would default to a 100 page document. Limiting Records per document to 1 forces 100 new, single page documents.)
How a bout to create two document, one is main template then select the frame/s and Edit>Place and link and paste it on the second document and when you do any change on the main document it can update on the second document.
Define text variables and use them.
Or use Data Merge.