Mail Merge one piece of data onto pdf.

If the letter is the same for all people then you can do it by extracting a single letter from the file, adding an ID Number field to it and then performing a Mail Merge on that file and the data file, using a script.

One such script is this (paid-for) tool I've developed that will allow you to do just that, and can even be used to automatically send out the letters to the employees, if you add a (hidden) field with their email address to the form:

https://www.try67.com/tool/acrobat-mail-merge-and-email-pdf-files

Create a field called ID on the first page of the PDF and place it where you want it.  Run the following script in the console:

var rc=this.getField("ID").rect;

Remove the field.  Next, create an array of the ID numbers like this:

var aray=[

12345,

678910,

11121314]

If the ID numbers contain any characters besides numbers they will need to be in quotes.  You can easily create this script in Excel by putting a formula in a cell that puts " at the beginning and ", at the end of a referenced cell containing the ID Number, then drag the formula all the way down, then copy and paste the column between [ ] in the console.  Remove the last comma after the last item in the array.

Next, run the following script in the console:

for(var i=0; i<this.numPages; i++)

{

var f=this.addField("ID."+i, "text", i, rc);

f.value=aray[i];

}

this.flattenPages();