Would you own the land if you possess the deed even if it belonged to another party? Like for instance, if thieves were to steal it before the owner was going to sell their home, would they still own the land, or does the thieves own it, or would the owner need to pay to get it back?
The land deed isn't just a description of land boundaries. It includes the owner's name, and usually includes the name of the person from whom the land was bought, unless it was bought from the crown/government, in which case it would usually indicate that instead.
So you couldn't just steal the land deed and try to claim that the land was yours, because the deed was going to have the rightful owner's name on it.
These aren't from Europe but here is a book of translated land deeds from 1600s New York. And here is a collection of scans of original deeds that those translations are based on.
As one example in the above linked book (Petrus Stuyvesant was the director of the "New Netherland" colony):
"Petrus Stuyvesant, on behalf of their High Mightinesses, etc... has given and granted to Jan Picolet a parcel of land lying on the South River of New Netherland south of Fort Casamier near the Brickmaker's Hook, between the plantations of Philip Jansz and Jacob Crabbe; running from the aforesaid Jansz' land west along the shore to the land of Jacob Crabbe 28 rods; along the land of the aforesaid Crabbe northwest 60 rods to the public highway; then along the aforesaid highway to the land of Philip Jansz west 30 rods; and then to the place of departure southeast by south 64 rods; making altogether 3 morgens and 85 rods, with the express conditions, etc,..
"Done at Amsterdam in New Netherland, 1 September 1656."
Probably more what your looking for is this publication which contains several land deeds in the county of Wiltshire, England, in the 1200s. You see records such as this:
"Robert Burnell, Bishop of Bath and Wells, grants to God and the Church of St. Mary of the Nuns, and to Claricia Prioress, in free alms, one acre of land in Kington St. Michael in the East Field, in the ploughed ground called 'Goldshawe,' between the land of the Prioress on the East, and land of Richard Carpenter on the West, with the Advowson of the Church."
This series of books of transcribed public records in England may also interest you. The books contain a variety of public records, only some of which are land deeds, so it will give you a taste of what these land deeds were like.