What is the Reformed perspective on "All people are called by God to salvation in Christ"? The quote in the title is taken from paragraph 16 of the JOINT DECLARATION
ON THE DOCTRINE OF JUSTIFICATION by the Lutheran World Federation and the Catholic Church. Is such a statement consistent or inconsistent with Reformed doctrine? If judged to be consistent, is it necessary to qualify the statement for it to fully harmonize with relevant doctrines?
A typical reformed response on this statement would be like that found in Matthew 22:14 “For many are invited, but few are chosen.” 

A typical reformed expositor writes:


  The gospel call goes forth far and wide. It reaches ever so many. Most of them are like the man in the parable: they hear but do not heed. In comparison with those many that are lost there are but few that are saved, that is, few that are chosen from eternity to inherit life everlasting. Salvation, then, in the final analysis, is not a human accomplishment but the gift of God’s sovereign grace. Cf. Luke 12:32; John 6:39, 44; Eph. 1:4. (NEW TESTAMENT COMMENTARY, WILLIAM HENDRIKSEN
  Exposition of the Gospel According to Matthew)


Regarding the article on Justification that is linked in your question, historical reformed teachers would most likely find it intellectually dishonest. The Protestant view of Justification occurs in a 'single moment' prior to any kind of moral ability to be had.  A Catholic view of justification is that it is a life time process similar to what a Protestant calls sanctification. The article entirely glosses over this division, while grouping statements which both agree to under vary different senses. The Reformers would condemn this article and probably accuse the authors of deceit. The Reformers were not that interested in unity when it came to the central doctrine of the gospel which they believed the Catholic church to have utterly corrupted by denying the justification of a sinner 'in a moment' prior to sanctification.