can i make superscript characters in "Adobe Acrobat Pro DC" ??

You are right I exagerated!  

I will show a picture. 

The first date (see image in yellow) works fine. The date is taken from a calander. 

Here is the script to add the er in superscript for the first date

var oDateValue = util.scand("d/mmmm/yyyy",this.getField("Date1_af_date").valueAsString);

var nJours = util.printd("d", oDateValue);
var cMois = util.printd("mmmm", oDateValue);
var nAnnee= util.printd("yyyy", oDateValue);

var DateComplete = nJours+ " "+cMois+ " "+nAnnee;
var MoisAnne = " "+ cMois + " "+ nAnnee;

var g = this.getField("DatteLettres_af_date");

if (nJours ==="1" && cMois !="")

{
// Create an array to hold the Span objects
var spans = new Array();
// Each Span object is an object, so we must create one
spans[0] = new Object();
spans[0].text = nJours;
spans[1] = new Object();
spans[1].text = "er";
spans[1].superscript = true;
spans[2] = new Object();
spans[2].superscript = false;
spans[2].text = MoisAnne.toLowerCase();
}

else{

event.value = DateComplete.toLowerCase();

}

// Now assign our array of Span objects to the field using
// field.richValue
g.richValue = spans;

For the second one, I have some issues. 

The text for the letter comes from an acroDialog. This allows to easily change the letter template. 

I applied some scripting and replace some terms with some variable results to update the letter.

End of script to display info into the letter:

var NewTexteLettre1_v = "";

NewTexteLettre1_v = TexteLettre1_v.replace(/AfficherPolitesseDeLaLettre/g,PolitesseArray1).replace(/AfficherDateOuverture/g, dateOuvertureR).replace(/AfficherMontantSansLotsAdjudicataireDeLaLettreSansQualite/g,NewMontantSSLotsAdj).replace(/AfficherGarantieDeLaLettre/g,AfficherGarantieL1).replace(/AfficherNonConformiteOuAdmissibiliteDeLaLettre/g, AfficherConformite1).replace(/AfficherAdjudicataireSSLotsQual/g,AdjudicataireSSLotsQual).replace(/AfficherLotsEtMontantsAdjudicataireDeLaLettreSansQualite/g,LotMontantAdjL1).replace(/AfficherLotsEtMontantsAdjudicataireAvecLotsSansQualite/g,TousAdjudicataireLots).replace(/AfficherNoteQualiteAvecQualiteSansLotsDeLaLettre/g,NoteQual1).replace(/AfficherMontantAdjQual/g,MontantAdjQual).replace(/AfficherMontantAjusteQual/g,PrixAjusteQual).replace(/AfficherRangNonAdj/g,rangLettre1R).replace(/AfficherNoteQualitéAdjudicataire/g,NoteQualAdj).replace(/AfficherSignataire/g,Signataire).replace(/AfficherTitreSignataire/g,TitreSignataire).replace(/AfficherInitiales/g,Initiales).replace(/AfficherMontantSansLotsAdjudicataireAvecQualite/g, MontantSSLotsAdjQualL1).replace(/AfficherMontantAjusteSansLotsAdjudicataireAvecQualite/g,MontantAjSLASAQL1).replace(/AfficherAdjudicataireSansLotsSansQualiteOuAvec/g,SoumisionnaireSSLots).replace(/AfficherAutresAdj/g,AfficherAutresL1).replace(/AfficherDuouDes/g,afficherDuouDesL1);

event.value = NewTexteLettre1_v;

My challenge:

How could I add the er in superscript in the letter?  I know how to add er but not in superscript in the second example, and I don't want to manually configure the letter like I did for the first date because there is a lot of info in the text field coming from the acrodialog. 

I think I would need to use something like this but I don't know how to adapt it to. Also where should i place the adapted  script, in the personalized format script?

Info from API reference 2017

// Custom Keystroke event for a rich text field.
var span = event.richChange;
for ( var i=0; i<span.length; i++)
{
span[i].text = span[i].text.toUpperCase();
span[i].underline = !span[i].underline;
span[i].textColor = (span[i].underline) ? color.blue : color.red;
}
event.richChange = span;

Hopefully I can get some help.   Thanks