Why Using FileToStr() to Load a PDF (or Other Binary File) in Visual FoxPro Is a Mistake

1. FoxPro strings are not binary-safe

• FoxPro strings are designed for text, not arbitrary binary data.
• When you use FileToStr(file.pdf), FoxPro assumes the bytes in the file represent text, and stores them as a character string.
• This leads to issues if the binary data includes:
  • Null bytes (0x00) — may terminate the string prematurely
  • Control characters — may be stripped or misinterpreted
  • 8-bit values ≥ 128 — may be re-encoded or altered due to character set conversion

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2. Binary data (like PDF files) may not be valid Unicode

• PDFs often contain arbitrary byte values that do not form valid text encodings (Unicode or otherwise).
• When FoxPro reads such a file into a string, it may:
  • Corrupt the data by interpreting byte sequences as characters
  • Substitute or drop bytes that don’t map cleanly to Unicode
• Result: the returned string is not byte-for-byte identical to the original file.

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3. Consequences of this mistake

• When you save that string into a MEMO or CHAR field:
  • The binary data may be irreversibly damaged
  • Exporting it back (e.g. with StrToFile()) may produce a broken PDF
  • Re-encoded characters may not match the original binary at all

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