The only truly secure way to erase the file from an SSD would be to use a tool provided by your manufacturer. Exporting the file to a RAM disk / USB stick will gain you no extra security at all.

Overwriting the file with OS tools improves things a litte. While the data is still physically present on the SSD, at least you can be sure that the sectors containing it were remapped and thus are inaccessible to OS file restore tools.

If I had something really important on the SSD which I had to erase, I would do a full backup, reset the SSD encryption key with e.g. `hdparm --security-erase` and then restore the data back.