I have encountered a bug in Acrobat Reader DC that is related to encoding of ECDSA digital signatures. The signature is composed of two numbers. It seems that when the highest bit of those numbers is set it is not padded with zero to make sure that the number is treated as positive integer. Instead it is treated as a negative integer. Adobe itself treats those signatures as valid, but other software refuses to accept them. Our nationwide eID uses ECC, so this bug impacts a large number of users. I can provide test file with valid and invalid signatures created using same ID-card.