Tool to remove image parts in PDF The reader of my university lecture regularly posts lecture notes online. The pdf contains handwritten mathematical theorems including the proofs. Everything is written on a completely white background. 

I want to create a new printable file containing the theorems and comments only (no proofs) as exam preparation

Is there an easy tool able to accomplish this on a Mac running High Sierra? It may be a bit tricky to get the breaks in pages right.  The workflow would ideally look like this:

Use rectangular selection tool to highlight proof. Hit some key to delete selected area/fill the rectangle white. Select everything below the proof and move it upwards until no whitespace is left.
Maybe think from the opposite side...


Open your PDF  
Select an area you want to keep.  
 Cmd ⌘   C  to copy, then  Cmd ⌘   N  which will open a new document with the clipboard contents.  
Repeat for each section you want to keep.  
Save each of your new sections as separate files. Use the default name, which will number in save order, these will be ephemeral.  
Close everything.  
Select all your newly-saved files in Finder &amp; Open  
They will all open in one window, in file order.  
You can then Print the whole lot as a single document - to PDF.


Requires Preview prefs > General > Open groups of files in the same window