If Finder lets you open files on a Windows drive but refuses to save changes back to it, check the format. macOS can usually read NTFS, but it does not provide normal NTFS write support. You can copy files off the drive without erasing it.

Confirm that the drive uses NTFS

Connect the drive and select it under Locations in Finder.
Press ⌘ + I and look for Format. A label such as Windows NT File System (NTFS) identifies the format.
If the drive is missing from Finder, open Disk Utility and choose View → Show All Devices. If macOS asks to initialise or erase a disk that holds needed files, cancel. If the disk opens normally on its original Windows PC, copy the files there first.

If Finder reports exFAT or APFS instead, check available space and the permissions on the destination. Apple lists several possible causes in its guide to drives that won’t save files.

Copy files from NTFS to your Mac

Check that the destination has enough free space. Create a new folder on the Mac or on a second drive you can write to.
On the NTFS drive, select the folders you need and press ⌘ + C. Open the destination folder and press ⌘ + V.
When the copy finishes, open several representative files from the destination. Check any copy errors and compare the source and destination folder sizes and file counts in Finder. Keep the original until you’ve verified the files you need.

Write files without changing the NTFS format

For an occasional transfer, copy the files from the Mac to a spare exFAT drive or a writable network share. Use a Windows PC to finish copying them onto the NTFS drive. If both computers can reach the same network, the share can save you a trip with a second disk.

For regular direct writes from your Mac, an NTFS driver is an option. Check your exact macOS version, Mac chip, and the driver’s installation requirements before paying or installing. Test copying, renaming, ejecting and reconnecting on a spare NTFS disk before using it with your only copy. Paragon’s product page lists its current compatibility and installation details.

Switch to a shared format after making a copy

For a drive you control and use with both Mac and Windows, exFAT is often the simpler long-term choice. Copy the files to a separate destination, verify the copy, then erase and reformat the original. Compare APFS, exFAT and NTFS and see the reformatting steps.