Don't know if you're still around, Cronos75, but here is a simple example of using the Open() function to create a new FrameMaker file.
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// This gives you a PropVals object with default values that you will feed to Open().
var oPropVals = GetOpenDefaultParams();
// These two lines set a value in the PropVals object that says this is a new file to create.
var i=GetPropIndex(oPropVals,Constants.FS_NewDoc);
oPropVals[i].propVal.ival=true;
// This gives you another PropVals object that Open() requires for some reason.
oRetParms = new PropVals();
// The full file path and filename of the FrameMaker file to use as a template for the new file.
// Use two slashes instead of one in paths.
sFilename = "C:\\Users\\myname\\dev\\template.fm";
Open(sFilename, oPropVals, oRetParms);
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Result: This opens an untitled file in FrameMaker that is based on the template file you supplied. The template could be any damn FrameMaker file you have sitting around.
Mark