Shortcut MacOS to go to the beginning of a document
AFAIK, there is no universal shortcut. But Preview provides for this with the "home" and "end" keys (on an extended keyboard). Another handy Preview shortcut is CMD-OPT-G, which brings up a tiny dialog where you enter the page number you wish to display.

For Word, or other apps, you might try creating your own shortcuts: System Prefs > Keyboard > Shortcuts . . . App Shortcuts.

G'luck.