Hi,
you can't change the behavior of the save button in the browser nor in Reader/Acrobat.
You can add a custom button within your form which calls a custom script from a folder level script using the browserForDoc method.
The browseForDoc methos is the only one whcih can change the name in the saveAs dialog.
Here's an example., you can run from Acrobat console.
You need to combine it with the solution from the other thread to make it work with your form.
http://forums.adobe.com/message/2266799#2266799%232266799
var oRetn = app.browseForDoc({
bSave: true,
cFilenameInit: "MyForm.pdf",
cFSInit: "",
});
if (typeof oRetn !== "undefined") {
this.saveAs({
cFS: oRetn.cFS,
cPath: oRetn.cPath,
bPromptToOverwrite: false
});
}