Anyone know of a good Windows file compare program?

Would like to compare two files and see if they are identical.  We are transmitting pdf's across a vpn and suddenly when they get to the destination Adobe Reader will not open them.  Source files open readily.  Would like to be able to prove yes or no that the files are being corrupted in transit or if it is something else going on.

Preference would be to be able to see the differences in hex, but a listing of the differences would do.

Obviously, would prefer free, but would consider a solution which is not.

This is for a Windows environment, I see that there are a few things out there for unix.

Also if anyone has any ideas as to what might be going on, would love to hear them.  This is quite strange...
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JohnBusiness Consultant (Owner)Commented:
I use WinMerge for files up to about 500 MB.   I like it because it gives a nice Files are Identical message. Free.

I use Beyond Compare for File and Folder compare. Good for multiple files in a folder.

I use Ultra Compare to compare any size of file. Good for Virtual Machine files 50 GB and up.
Potentially you have corruption issue I.e. During the VPN something like anti-virus on the other end interrupts transmission.
You can use Gpg' md5 or other tools that you can generate a signature before sending. When received the same process should result in the same signature . If sig differs, the file did not arrive as it was sent.
Lee W, MVPTechnology and Business Process AdvisorCommented:
I agree with arnold - create a hash before transmission, then again after transmission.  If they don't match, there's a problem.

Consider zipping it.
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
Of course hashing or zipping requires to have remote access like with RDP, otherwise it is utterly inefficient (requiring essentially to copy it again in memory). IMO zipping works best as users are used to it, and it tells if the file is corrupt directly. Hashing requires extra steps you need take, including performing the check.

If you use RoboCopy for copying, at least existence and metadata will be checked, so correct length is guaranteed. It might suffice here.
Tom CieslikIT EngineerCommented:
Best software I know and use everyday is CompareIt


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Dr. KlahnPrincipal Software EngineerCommented:
Microsoft WinDiff from one of the Support Tools CDs, if you want to actually see what the difference is.

If you only want to know if there is a difference, then per previous suggestions hash it before and after.
Dr. KlahnPrincipal Software EngineerCommented:
Points divided among participants.  All suggestions are valid.
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