Snipmages and .DAT files

I have Windows 7, Office 10 both Home Premium and use Incredimail for emails on both my laptop and my PC. Why when my accountant sends me a snip image it arrives in my inbox perfectly on my Laptop and in my PC it is just an embedded formula (url) not a snip image. Similarly some pdf files arrive perfectly as a pdf on my laptop but on my PC some files (sent as pdf) arrive in my inbox as a .dat file yet both my laptop and pc use exactly the same software and opersting system. Can you please help

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