Moving files from windows PC to Mac desktop

You have a few of options:

1) Migrate as per > Transfer from PC to Mac with Migration Assistant - Apple Support

2) use file sharing to copy important data files from the PC to the Mac.

3) Use an external storage to move your data files over.

I suggest seriously studying each options and then choose the one that best suits your case.

Yes, you can copy files from the PC's external HD to the Mac. Millions have come before you and doing this type of migration is how I started well over 20 years ago now.

However you cannot copy PC apps though. For example the PC versions of MS Word and Excel will not run on your new Mac. You need to buy the Mac OS version or subscribe to MS's subscription based apps. All of your PC based files like Word and Excel files will run just fine once you have installed the Mac OS equivalent such as Office for Mac. You can also use Apple's Pages and Numbers apps to open and edit MS Office documents. There are also free web based apps that will open and edit your MS Office documents too, for example Libre Office.

For your e-mails that migration may be a little more challenging. IF it were me, I'd use your ISP's web based portal and then use the Mac's Mail app and it will download all of your e-mail. For example, I happen to use Comcast as my ISP (my wife uses Gmail) so just make sure your mail is on the ISP's site and then use the Mail app on the Mac, which is extremely easy to setup and use by the way!!!!!!!!!!!!!!!!!!!

You're welcome.