Can a pre made jam be thickened into pate de fruit?
Here is a discussion on Jam to Pate de Fruit? at eGullet Forums.
Question posted by pastryani:

Is it possible to make PDF from jam or jelly?  Jam is essentially a more fluid version of PDF, so I would think that I could either (1) boil off extra liquid from the jam until it's thicker, or (2) warm the jam and add a bit of pectin to it to thicken it.  If I were to try the latter, anyone know what amount of pectin would be needed?  Thanks!

One answer by ElainaA:

I've done (an unsophisticated) PDF from jam many times. The recipe is from one of the first candy books I bought, years ago, Weinstein's The Ultimate Candy Book. It uses gelatin: 2 envelopes of unflavored gelatin, softened in 1/3 cup. 3/4 c. granulated sugar and 1/3 c. water combined and heated to a boil. 1 c. jam or marmalade stirred in to dissolve, gelatin added, bring to a boil and cook 2 minutes. Pour into an oiled pan and refrigerate until set.
There is a very similar recipe in Ruth Kendrick's Candymaking called 'fruit jam jellies'.
I'm not sure if these are true PDF but they are good. I've made both with various types of jam or jelly. I preserve so much I have to do something with it.

Conclusion: It is indeed possible, and not hard to do.