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Is there a way to write data to a file in the font that was used in the software
This makes non sense, it look like a big misconception.
Chars stored in a file are no related to a font, not even remotely.
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I use an ascii shift cypher to give a low level of encryption.
What you describe is a variant of ROT 13 encoding or a XOR cypher, both are probably the simplest way to encode text, but they are also the easiest to break. People used to this kind of coding can read the text directly without even decoding it.
ROT13 - Wikipedia[
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XOR cipher - Wikipedia[
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