You can use:
from itertools import combinations
df = df.set_index('Dt')
cc = list(combinations(df.columns,2))
df = pd.concat([df[c[1]].sub(df[c[0]]) for c in cc], axis=1, keys=cc)
df.columns = df.columns.map(''.join)
print (df)
AB AC AD BC BD CD
Dt
11-apr 0 0 0 0 0 0
10-apr 1 -1 0 -2 -1 1