If you have .VHD virtual disk from one of the Microsoft virtual products and you want to convert it to .VMDK by VMware, this you can be done using a conversion tool. There are two methods that you can follow depending on your scenario:

Method A: VMware vCenter Converter Standalone

Use a converter software product by VMware which is free to download using the link below:

http://downloads.vmware.com/d/

You can use this if your .VHD virtual machine is:

1. Powered-on machine or
2. Hyper-V Server

Method B: StarWind V2V Converter

If your .VHD is not in any of the above cases (i.e. backup image) then you can use StarWind software tool to do this conversion. I like this product as it is free to use, simple and does the job. You can download it from this link: http://www.starwindsoftware.com/download-starwind-converter

If you run into problems or have any other related queries, please write in the comment.

If you have a .VMDK virtual disk and you want to convert it to .VHD use Method B:

For Method A, read this post

Method A: VMware vCenter Converter Standalone

You can use a converter software product by VMware which is free to download using the link below:

http://downloads.vmware.com/d/

You can use this if your .VHD virtual machine is:

1. Powered-on machine or
2. Hyper-V Server

Method B: StarWind V2V Converter

If your .VHD is not in any of the above cases (i.e. backup image) then you can use StarWind software tool to do this conversion. I like this product as it is free to use, simple and does the job. You can download it from this link: http://www.starwindsoftware.com/download-starwind-converter

If you run into problems or have any other related queries, please write in the comment.