Extendscript - How to make a specific document active?

Actually that was the way I had tried. But the formatting is not happening in the docs: I have shared the code below: Could you please help me?

var i=0;
var ind=getFontIndex ("Calibri");
var ptag, ptagFormat, ptagFormatName, ptagsSize;
var newpara, oldpara;
var ctags =[];
var ptags =[];
var ctag, ctagFormat, ctagFormatName, ctagsSize;
var newchar, oldchar;
var dc=app.FirstOpenDoc;

while(dc.ObjectValid())
{

changePgFormat(dc);
changeChFormat (dc);
dc=dc.NextOpenDocInSession;
}

function changePgFormat(DocName)
{
ptagFormat= DocName.FirstPgfFmtInDoc ;

while (ptagFormat.ObjectValid() == true)
{
ptagFormatName = ptagFormat.Name;
// alert(ptagFormatName);

ptags.push(ptagFormatName);
ptagFormat=ptagFormat.NextPgfFmtInDoc;
}
ptagsSize = ptags.length;
//alert ("Number of formats in array before processing: " +ptagsSize);

for(i=0; i<ptagsSize; i++)
{
ptagFormatName = ptags[i];
newpara = doc.GetNamedPgfFmt (ptagFormatName);
newpara.FontFamily=130;
}

for(i=0; i<ptagsSize; i++)
{
ptags.pop();
}
ptagsSize = ptags.length;
//alert ("Number of formats in array after processing: " +ptagsSize);
}

function changeChFormat(DocName)
{
ctagFormat= DocName.FirstCharFmtInDoc;
while (ctagFormat.ObjectValid() == true)
{
ctagFormatName = ctagFormat.Name;
ctags.push(ctagFormatName);
ctagFormat=ctagFormat.NextCharFmtInDoc;
}
ctagsSize = ctags.length;

for(i=0; i<ctagsSize; i++)
{
ctagFormatName = ctags[i];

if(ctagFormatName!="Symbol"){
newchar= doc.GetNamedCharFmt (ctagFormatName);

newchar.FontFamily=ind;

}
}

for(i=0; i<ctagsSize; i++)
{
ctags.pop();
}

}

function getFontIndex(fontName)
{
var fname=app.FontFamilyNames;
var fLen = fname.length;
for (i=0; i<fLen; i++)
{
if(fname[i]== fontName)
{
return i;
}
}
}