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).

You can retrieve the FASTA text from the snap gene viewer itself. Click 'Sequence' on the bottom left and then click 'Use compact format' on the middle far left.