pbmtopgm, pbmtoplot, pbmtoppa, pbmtoptx, pbmupc, pgmenhance: add pages (#12224)

pages/common/pbmtoppa.md

@@ -0,0 +1,12 @@
+# pbmtoppa
+
+> Convert a PBM image to HP Printer Performance Architecture format.
+> More information: <https://netpbm.sourceforge.net/doc/pbmtoppa.html>.
+
+- Convert a PBM image into a PPA file:
+
+`pbmtoppa {{path/to/image.pbm}} > {{path/to/output.ppa}}`
+
+- Specify the desired dots-per-inch and paper size:
+
+`pbmtoppa -d {{300}} -s {{a4}} {{path/to/image.pbm}} > {{path/to/output.ppa}}`