Sample Files by Technology Channel
Windows line endings (CRLF)

Line endings are a quieter source of trouble.
Windows traditionally ends lines with a carriage return and line feed, while macOS and Linux use a line feed alone.
Diff tools, parsers and checksums can all behave differently depending on which one they meet.

Good test files also come in families. A single PDF tells you that your viewer can open a PDF; a family of PDFs tells you how it copes with one page and a hundred pages, with a few kilobytes and ten megabytes, with plain text, scanned images, form fields and passwords. Testing across a family is how you find the edges of a system before your users do.