Looking for some insight to what i have done editing a pdf

[Graemezee1]

I was provided with a print file with several hundred pages   I was asked to remove the fold indicator ( A dotted cyan line across the centre of the page )  I wondered if  I could remove the cyan plate but this did not seem to be an option. So I started the manual process in edit pdf. 
On page one the line came off simply. On page two  I could not select the line  I Could only select a panel which covered half the page which did not seem to be relevant to the content so I deleted it hoping to gain access to the line below.  deleting the panel deleted the line, and somehow the blue fold line had been removed from all the other pages.

I wondered if the panel was some kind of layer and I have been able to delete the layer from the whole document.  In truth, I have no idea what I have done but would like to know as this could be very useful. 

[Document Geek]

Can you post a few pagesfrom the document so we can take a closer look?

[Graemezee1]

Attached, a before and after file including the first 3 pages.   I have removed the Corporate logo from the file 

[Jeffrey_Smith]

As for layers, many times a document is created in Indesign with layers, one for art, second for fold guide. The PDF would need to have "Create Acrobat Layers" selected for ID layers to convert into Acrobat layers. If that was the case, you could hide the fold layer. Check the Layers pane in Acrobat to see if there are any.

[Graemezee1]

Hi, I have checked the layers panel  there are none.

[Jeffrey_Smith]

Sometimes the fold art is made visible and non-printing, have you checked print attribute of the blue line?

[Graemezee1]

Hi, the Line is visible and printing 100% Cyan.  What really intrigues me is how deleting the line on page two removed the line from hundreds of other pages. I am grateful I did not have to do this manually.  I have been using Acrobat  in a prepress environment since  version 1 was released  Grantedly back in the day it was with QuarkExpress  but  I have never  had  something  like this happen. 

[Bernd Alheit]

You can use the redaction tool for this.