Using FileMaker Pro Advanced > Copying or moving fields between tables (FileMaker Pro Advanced)
 
Copying or moving fields between tables (FileMaker Pro Advanced)
You can copy fields from one table and paste them into another table in the same file or a different file. Field data is not copied.
1. Choose File menu > Manage > Database > Fields tab.
2. Select the field that you want to copy.
3. Click Copy, then click OK.
4. In the Fields tab of the same file or a different file, for Table, choose the table where you want to paste the field.
5. Click Paste, then click OK.
Notes 
FileMaker Pro Advanced retains data source references to fields if they are valid when you paste. If you copy multiple fields that reference each other, copy them in one step to retain the references. If you copy them one at a time, the references may be lost. Check all data source references after pasting to ensure they are valid.
To copy and paste fields, you must have full access privileges to the source and destination files.
There is a difference between duplicating and copying a field: Duplicate duplicates a field within the current table. Copy makes the field available for pasting to another file.
Related topics 
Copying or importing table schemas (FileMaker Pro Advanced)