title: Convert multipage PDF to PNG and back (Linux)
body: <p>I have a lot of PDF documents that I want to convert to PNG, edit in Gimp, and then save back to the multipage Acrobat file.  I'm filling out forms and adding scanned signature, trying to avoid printing, signing, then scanning back in, with the ability to type the information I need to enter.</p>
  
  <p>I've been trying to use Imagemagick to convert to png files, which seems to work fine.  I use the command   <code>convert -quality 100 -density 300x300 multipage.pdf single%d.png</code><br>
  (I'm not really sure if the quality parameter is right for png).</p>
  
  <p>But I'm having problems with saving back to PDF.  Some of the files have the wrong page size, and I've tried every command and procedure I can find, but there are always a few odd sizes.  The resolution seems to vary so that it looks good at a certain zoom level, but either a few pages are specified at about 2" wide, or they are 8.5x11 but the others are about 35" wide.  I've tried making sure Gimp had the canvass size and resolution correct, and to save the resolution in the file, but that doesn't seem to matter.</p>
  
  <p>The command I use to save the files is <code>convert -page letter -adjoin single*.png multipage.pdf</code>   I've tried other parameters, but none seemed to matter.</p>
  
  <p>If anyone has any ideas or alternatives, I'd appreciate it.</p>