Update cheatsheets

pnmtoddif

@@ -0,0 +1,17 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# pnmtoddif
+
+> Convert a PNM image to a DDIF image file.
+> More information: <https://netpbm.sourceforge.net/doc/pnmtoddif.html>.
+
+- Convert a PNM image to a DDIF image file:
+
+`pnmtoddif {{path/to/image.pnm}} > {{path/to/image.ddif}}`
+
+- Explicitly specify the horizontal and vertical resolution of the output image:
+
+`pnmtoddif -resolution {{horizontal_dpi}} {{vertical_dpi}} {{path/to/image.pnm}} > {{path/to/image.ddif}}`