replace pdftk with qpdf

README.md

@@ -13,7 +13,7 @@ picture per page.
 This utility requires the following tools to be installed:
 
 ```shell
-apt install imagemagick pdfjam pdftk
+apt install imagemagick pdfjam qpdf
 ```
 
 ## Installation

photos2pdf

@@ -407,7 +407,8 @@ for png in "$outdir/"*.png ; do
         warning "Could not convert \"$png\" to PDF; skipped."
         rv=1
         continue
-    elif !  pdfjam \
+    elif ! \
+        pdfjam \
             --quiet \
             --outfile "$tmpdir" \
             --paper "$paper" \
@@ -419,10 +420,10 @@ for png in "$outdir/"*.png ; do
         warning "Could not align \"$pdf\"; skipped."
         rv=1
         continue
-    elif ! pdftk \
+    elif ! qpdf \
         "$jammed" \
-        stamp "$backdrop" \
-        output "$backdropped"
+        --overlay "$backdrop" \
+        -- "$backdropped"
     then
         warning "Could not watermark \"$pdf\"; skipped."
         rv=1
@@ -436,7 +437,12 @@ while read -r pdf ; do
     input+=("$pdf")
 done < <(ls -- "$tmpdir/"*.backdropped.pdf)
 
-if ! pdftk "${input[@]}" cat output "$pdfdir/$result_filename" ; then
+if ! \
+    qpdf \
+        --empty \
+        --pages "${input[@]}" \
+        -- "$pdfdir/$result_filename"
+then
     warning "Could not concatenate \"$result_filename\"."
     rv=1
 elif ! "$keep_tmpfiles" ; then