Can someone help me identify this rock? Also, will it react to acid?
Your rock looks like limestone with an inclusion of re-crystallized calcite (The white part). A hardness test would help confirm the identification but reaction to acid is a strong indication of limestone.
From what I can make of the background there is even more limestone on the ground, either from a talus slope on a mountain or perhaps large crushed rock. Limestone is commonly used for surfacing driveways, it is also mined in large quantities for the production of lime and quick lime used in the manufacturing of cement and mortar.
Can I ask for some more specific information on where in Macedonia your sample was collected? What type of location, etc.
Edit: I miss read the question, in particular about the acid test. I thought an acid test had been completed and there was a positive reaction. My answer depends on a positive acid test. If the acid test was not completed I wouldn't depend on my answer.