Add useful PDF editing commands.

pdf.md

@@ -6,3 +6,12 @@
 ### Remove password
 ```pdftk input.pdf input_pw <password> output output.pdf```
 
+### Extract PDF from signed P7M
+```openssl smime -verify -noverify -in input.pdf.p7m -inform DER -out output.pdf```
+
+### Remove images from PDF
+```cpdf -draft input.pdf -o out.pdf```
+
+### Increase contrast, compress and make PDF from JPEGs
+```convert -quality 30 -brightness-contrast -5x10 -density 150 src/input-*.jpeg -compress jpeg output.pdf```
+