Dear Sudeep,

Hope you are doing great.

These are few links where you can convert the sequences into Fasta Format.

http://avermitilis.ls.kitasato-u.ac.jp/readseq.cgi

https://molbiol-tools.ca/Convert.htm

https://www.ebi.ac.uk/Tools/sfc/emboss_seqret/

In case if you are not convenient in using these tools,

You can directly search the GENE/PROTEIN in NCBI database and in Genomic regions, transcripts, and products section, you can get the Fasta format by just one click.

Regards,

Sanketh Dhumal S

You don't need any software. In Snapgene, simply go the the file option > export > DNA > choose the file format > save the file in desired format (.fa, .fas, .fasta for you).