When you have a damaged PKG file for Mac OS, it is most likely that some (or several) of the following issues are causing it:
In the case when the operating system configuration is causing issue with opening PKG file then you can do a brief procedure in the system security configuration:
With these simple steps you can open the PKG file from the identified developers.
In the case when you verify that the file is actually damaged then you must proceed as follows.
You should know that PKG files because they are installable files, if they are damaged, it is very likely that it won’t be possible to repair them. Therefore, you should try to download the file again, if possible, from the vendor’s site. Before doing so you can try to repair a drive on which the file is located to see if it may repair it.
If "Disk Utility" reports that there are "overlapping extensions assignment" errors, two or more files occupy the same disk space and it is likely that at least one of them is damaged. You should check each file in the list of affected files. Most files have aliases in a “DamagedFiles” folder, on the top level of the disk.
If you can replace a file or recreate it, delete it.
If it contains necessary information, open it and examine its data to make sure it is not damaged.
If Disk Utility cannot repair the disk or you receive a report stating that the "First Help" process has failed, try repairing the disk or partition again. If this is not useful, make a backup copy of all possible data, reformat the disk, reinstall macOS, and then restore the backup data.