Writing code that will manipulate pgm files - c++

Question

I am trying to do a program that will run with a header file to manipulate pgm files.
I have the header file below, I just am stuck on how to write all the functions to actually make it work.
/* Header file to define the PGM class, that lets you manipulate PGM files.
The files themselves are simply stored in a vector of vectors of ints.
All of the methods return true if they succeed and false if they fail.
Write() needs to produce files in a specific format:
- P2 on its own line, no spaces.
- cols rows on the next line, separated by a space, no additional spaces
- 255 on its own line, no spaces.
- Then the pixels: 20 pixels per line, one space between pixels, no additional spaces.
- We don't print additional newlines at the end of each row of pixels -- just
start the next row of pixels.
- The last line is the only one that can have fewer than 20 pixels.
*/
#pragma once
#include <vector>
class Pgm {
public:
bool Read(const std::string &file); // Reads a PGM file
bool Write(const std::string &file) const; // Writes a PGM file
bool Create(size_t r, size_t c, size_t pv); // Creates a rxc PGM with the given pixel value
bool Clockwise(); // Rotates 90 degrees clockwise
bool Cclockwise(); // Rotates 90 degrees counterclockwise
bool Pad(size_t w, size_t pv); // Adds a border of w pixels with the given value
bool Panel(size_t r, size_t c); // Makes rxc copies of the PGM
bool Crop(size_t r, size_t c,
size_t rows, size_t cols); // Crops from r:c to (r+rows):(c+cols)
protected:
std::vector < std::vector <int> > Pixels;
};