/usr/include/libdigidoc/ is in libdigidoc-dev 3.10.1.1208+ds1-2.1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libdigidoc/DigiDocCert.h
/usr/include/libdigidoc/DigiDocConfig.h
/usr/include/libdigidoc/DigiDocConvert.h
/usr/include/libdigidoc/DigiDocDebug.h
/usr/include/libdigidoc/DigiDocDefs.h
/usr/include/libdigidoc/DigiDocDfExtract.h
/usr/include/libdigidoc/DigiDocEnc.h
/usr/include/libdigidoc/DigiDocEncGen.h
/usr/include/libdigidoc/DigiDocEncSAXParser.h
/usr/include/libdigidoc/DigiDocError.h
/usr/include/libdigidoc/DigiDocGen.h
/usr/include/libdigidoc/DigiDocHTTP.h
/usr/include/libdigidoc/DigiDocLib.h
/usr/include/libdigidoc/DigiDocMem.h
/usr/include/libdigidoc/DigiDocOCSP.h
/usr/include/libdigidoc/DigiDocObj.h
/usr/include/libdigidoc/DigiDocParser.h
/usr/include/libdigidoc/DigiDocSAXParser.h
/usr/include/libdigidoc/DigiDocService.h
/usr/include/libdigidoc/DigiDocStack.h
/usr/include/libdigidoc/DigiDocVerify.h