You can use the DOS-command TYPE and MORE to get the first megabytes or gigabytes of a large file e.g. of TXT, XML, CSV etc.
This is done by piping the result into another file, there by getting only the first part of the file piped into the new file.
The DOS-command below will start piping the large file into the smaller new file.
type LARGE_SOURCE_FILE | more > SMALL_DESTINATION_FILE
You are not able to see the result from the DOS-command. You need to press the SPACE-key on your keyboard, because every time you press the SPACE-key a new page of the file will be showed and thereby piped into the SMALL_DESTINATION_FILE.
When you think you have done this enough times, then you have to press CTRL-C on your keyboard, this will terminate the type-command and you will have the SMALL_DESTINATION_FILE containing data from the LARGE_SOURCE_FILE.
Be aware that you will get the — more — pipe text in the file!