Well – it depends.
If the original will was last known to be in the possession of the testator, then it is presumed that the will was destroyed by the testator with the intention of revoking it. In simple words, that the willmaker destroyed it, with the intention it would no longer operate as a will.
This is the very reason that we recommend that our clients leave their original wills with us, in our safe custody.
Where an original will cannot be found, but it can be shown that the will was not in the possession of the deceased testator and a copy exists, then the court can admit to probate a copy of the lost will.
In the case of famous Australian artist Brett Whitely, his will could not be found after his death, nor was there available a physical copy. But the court was satisfied about the content of the lost will, and that content was granted to probate.