merge several different files into a single file using c#

Question

I need to combine multiple files (video & music & text) into single file with a custom file type (for example: *.abcd) and custom file data structure , and the file should only be read by my program and my program should be able to separate parts of this file. How do this in .net & c#? -- my file has any size , for example 300 MB , 500 MB or 1 GB and merged file's size is about 1.5 or 2 GB , how i do it ? .. (using stream or memory stream ?!!)

 

 

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My program is similar to Microsoft Power Point .in pptx file you can put your texts and videos and then save the file with *.pptx format and load it anytime...