I want to know the best program to use to download .7z file
Are you asking about any .7z file or a specific .7z file. Generally speaking the type of file doesn't determine the best method of download. It would be more important to know how on the internet the file is made available.
You mean how to open a 7z file? http://www.7-zip.org/
If you need more help, please tell us how this is related to Adobe software.
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