Press Windows + E
Click This PC
Check Local Disk (C:) free space
You need at least 20–25 GB free for major updates.
If low:
Delete large files in Downloads
Empty Recycle Bin
Uninstall unused programs
Run Windows Update Troubleshooter
Open Command Prompt as Admin and type:
sfc /scannow
Right-click a PDF file
Click Open with → Choose another app
Select:
Microsoft Edge (for PDF)
Photos (for JPEG)