Hello Lau ,
Sorry to say, We are not sure about CHK files.
If those files are just renamed to chk, then You can change the file extension to .axx . Now try to open the encrypted files with the AxCrypt app. Because AxCrypt encrypted file has a file structure. If the file structure is not exactly same, then the AxCrypt app won’t open those encrypted files.
If the file contents are damaged or file format changed, then there is no use with the file. AxCrypt can open only the .axx and AxCrypt file structured files.