PDF Portable Document Format

SIGNATURE = bytes.fromhex("255044462d")
OFFSET = 0

def is_pdf(path: str) -> bool:
    with open(path, "rb") as f:
        f.seek(OFFSET)
        head = f.read(len(SIGNATURE))
    return head == SIGNATURE

const SIGNATURE = [0x25, 0x50, 0x44, 0x46, 0x2d];
const OFFSET = 0;

// bytes: a Uint8Array / Buffer holding the start of the file
export function isPdf(bytes) {
  return SIGNATURE.every((byte, i) => bytes[OFFSET + i] === byte);
}

package fileid

import "bytes"

var ispdfSignature = []byte{0x25, 0x50, 0x44, 0x46, 0x2d}

const ispdfOffset = 0

func IsPdf(b []byte) bool {
	end := ispdfOffset + len(ispdfSignature)
	if len(b) < end {
		return false
	}
	return bytes.Equal(b[ispdfOffset:end], ispdfSignature)
}

const SIGNATURE: &[u8] = &[0x25, 0x50, 0x44, 0x46, 0x2d];
const OFFSET: usize = 0;

fn is_pdf(bytes: &[u8]) -> bool {
    bytes.get(OFFSET..OFFSET + SIGNATURE.len()) == Some(SIGNATURE)
}

<?php
$signature = "\x25\x50\x44\x46\x2d";
$offset = 0;

function is_pdf(string $bytes): bool {
    global $signature, $offset;
    return substr($bytes, $offset, strlen($signature)) === $signature;
}