Malicious File

An adversary may rely upon a user opening a malicious file in order to gain execution. Users may be subjected to social engineering to get them to open a file that will lead to code execution. This user action will typically be observed as follow-on behavior from Spearphishing Attachment. Adversaries may use several types of files that require a user to execute them, including .doc, .pdf, .xls, .rtf, .scr, .exe, .lnk, .pif, .cpl.
Adversaries may employ various forms of Masquerading on the file to increase the likelihood that a user will open it.
While Malicious File frequently occurs shortly after Initial Access it may occur at other phases of intrusion, such as when an adversary places a file in a shared directory or on a user's desktop hoping that a user will click on it. This activity may also be seen shortly after Internal Spearphishing.
There are so many files available for gaining Execution on our target machine and creating payloads for them is just not possible to follow one methods since there are plethora of ways to create these and using different languages, but here I recommend a GitHub page with some POC of these famous extensions and are harmless as they only pop calc.exe