passage de 2 à 3..ça coince

Google translate (as this is the Enlish part of the forum):

Hello

I am on 2.3.2 Ubuntu 18.10 and I have 2.1

I can not read a file received by e-mail, whose first line is mscx (attached file)
? xml version = "1.0" encoding = "UTF-8"?
museScore version = "3.01"
programVersion3.0.1programVersion
programRevision06a66a2programRevision

and that I stayed in
/ Home / leleu / Documents / bobby / associat / CNA / amcpi / 2018-2019 / 2019-03-14

With 2.3.2 I have a message "permission denied" Yet the owner is "me" with all rights
With 2.1 I have a message recommending me to update my Musescore

my musescore 2.3.2 sees the demos housed in
/usr/share/mscore-2.3/demos, whose owner is root
and whose first lines of the mscx are
? xml version = "1.0" encoding = "UTF-8"?
museScore version = "2.01"
programVersion2.0.0programVersion
programRevision3543170programRevision
score +
LayerTag id = "0" tag = "default" LayerTag
currentLayer0currentLayer

I will "consult" a neighboring Windows that I must first upgrade

Indeed, MuseScore 2 can't open scores created or last saved with with MuseScore 3.
MusicXML export on 3 and import in 2 is the solution, see attached