pdfunite: Add page (#1633)

pages/common/pdfunite.md

@@ -0,0 +1,11 @@
+# pdfunite
+
+> PDF merging utility.
+
+- Merge 2 PDFs into a single PDF:
+
+`pdfunite {{path/to/fileA.pdf}} {{path/to/fileB.pdf}} {{path/to/merged_output.pdf}}`
+
+- Merge a folder of PDFs into a single PDF:
+
+`pdfunite {{path/to/directory/*.pdf}} {{path/to/merged_output.pdf}}`