A family of Microsoft word processing software products for creating web, email, and print documents.
As the saying goes, "There's more ways than one to skin a cat"
The low tech way would be to use mail merge for which you would create a Word Document with a table, or an Excel spread sheet in the first row of the table or spread sheet which you have a name for each piece of data (clients name, number, etc.) and you have the data in a subsequent row. Then you use that Word document or workbook as the data source for each of the documents and you insert the relevant mergefields at the locations in the document where the data is required.
Then there are numerous other ways, which involve the use of Visual Basic for Applications.