Guild Wars 2

As the title stats can you get a precursor drop from combining lets say 4 shoes. Or combining 3 shoes + 1 glove. This is because I am assuming 4 shoes only guarantees you shoes. And by putting glove in the forge you get a random item.

No
Precursors are weapons.. You cannot get weapons from armor.
If you want to try and forge a weapon – use weapons.
Ofc if you want a specific weapon, then use 4 of the same type of weapon.

If you use armor, then you will get armor back.

You can also use 3 weapons and 1 mystic forge stone, that will always give you a weapon.

3 armour and 1 weapon (rare) gives a chance of any exotic (armour, jewelery or weapon).
Could be a precursor if your luck is good. Most likely some form of rare.
4 armour only give armour back (random armour but still armour).