It's in the Library, of course, but what does the SSPX leadership think of it? This paragraph seems, for me, to sum things up nicely:
"We considering a matter of this kind to be of so grave and perilous a nature that even the Roman Pontiff, who is the viceregent of God and the Lord Jesus Christ upon earth, having a plenitude of power over nations and kingdoms, judging all and being judged of none in this present world, may nevertheless be reproved if he is found deviating from the faith-and (considering moreover) that where there is greater danger there should be also a fuller and more diligent consultation, lest false prophets or others having secular jurisdiction also, should entangle miserably the souls of the faithful, and should draw down with them into perdition and destruction the innumerable peoples committed to their charge and government in spiritual or temporal matters, and so it might happen that we should see the abomination of desolation spoken of by Daniel the Prophet, in the holy place. We therefore desiring as far as with God's help we can, in virtue of our pastoral office, to capture the foxes who seek to destroy the Lord's vineyard and to drive the wolves from the fold; lest we should seem like dumb dogs unwilling to bark and be compared to bad husbandmen and mercenaries;" (Cum ex Apostolatus Officio, 1)
This is not a discussion about sedevacantism, so if you would please, let's restrict this to the SSPX's views on this document.