Why do PDF imports have a clipping mask?

[#1]

I do not understand why the majority of the time I import very simple polygons and lines in PDF format and they all have clipping masks.

There is no  reason for there to be clipping masks on these PDF files, but it seems that Adobe automatically adds clipping masks for no reason. 

I have to go through the tedious process of looking for every clipping mask and one by one unclip them.

The clipping masks tends to span the entire document size.

There are the steps I have to go through to "process a file"

1) Go through layers panel and unclip all clipping masks one by one.

2) Go to the 4 corners of each document and delete all the nodes on each corner for every shape present.

[#2]

I do not understand why the majority of the time I import very simple polygons and lines in PDF format and they all have clipping masks.

There is no  reason for there to be clipping masks on these PDF files, but it seems that Adobe automatically adds clipping masks for no reason. 

I have to go through the tedious process of looking for every clipping mask and one by one unclip them.

The clipping masks tends to span the entire document size.

There are the steps I have to go through to "process a file"

1) Go through layers panel and unclip all clipping masks one by one.

2) Go to the 4 corners of each document and delete all the nodes on each corner for every shape present.

[#3]

The pdfs with clipping mask were certainly not made in Illustrator with Illustrator editing capabilities checked.

They are converted from PDF to Illustrator file format, and these clipping mask may sometimes be there for a good reason.

Make sure that no fill or stroke is selected in the tools panel and choose Select > Same Fill & Stroke 

Then just delete the selected objects.

[#4]

@Ton_Frederiks - That is not correct. I have created PDF files directly from Illustrator (or InDesign) and when I open them back up in Illustrator they will have clipping paths around either the whole document or possibly elements within the document.

[#5]

THe argument was not "made from Illustrator" but "made from Illustrator with editing capabilities checked". There is a huge difference between these two.

Please see this about Illustrator files: https://youtu.be/IpDh8Y7q8yE

[#6]

It makes clipping masks either way. Or, alternatively, creates extra space around objects that shouldn't be there. As if there were invisible points floating around.

[#7]

Please tell us about your issue

Please tell us where the file originates from

Which options were selected when you saved it

Any error warnings when you opened it

What's in the file

[#8]

Keep also in mind that Illustrator is not a PDF editor.

That is why you get unexpected results when you do so.