You can Import the contents of a text file into filemaker. The results may or may not be what you want, however. You can import your text file into fields in a table in filemaker. Filemaker will attempt to break up the text into separate fields and records based on the characters present in the file.
If you import the data as a tab delimitted file, each tab character will be treated as the separator dividing one field from another and each carriage return will be treated as the separator between records.
If you import the data as a comma separated file, you have similar results except that the comma instead of the tab character will be treated as the "field separator".
You can also insert the file or a reference to the file into a container field. That may be more what you are looking for. Can you say more about how you want to use this text file?