I have 2 powerpoint, I want to autoupdate the 2nd powerpoint while I edit the 1st

You could use the "relational" presentation technique

@Create a custom PowerPoint presentation from a set of slides -
http://www.techrepublic.com/blog/msoffice/create-a-custom-powerpoint-presentation-from-a-set-of-slides/884
Custom presentations enable you to deliver a selection of slides from your main show -- handy if you're pressed for time or need to tweak the information for a particular audience. See how easy it is to build and run a custom presentation.
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@ Intro- The Alternative to Traditional PowerPoint
http://www.indezine.com/articles/relationalpresentations.html
Short 2 page overview with a link to Aspire site
Five minutes into her presentation, the speaker realized something was very wrong. For several days she had been addressing groups of teachers at the primary school-level. Unfortunately on this day, a scheduling glitch had occurred. Seated before her were secondary school teachers—and that the entire full-day seminar about to be delivered, was irrelevant to them!
The speaker quickly assessed the situation and then used the “switchboard” to completely change the focus of her talk on the spot! With barely a bump in rhythm, she navigated away form the primary school material and chose secondary school tracks relevant to her audience. It was beautiful to watch and demonstrated the dramatic potential of what years later came to be known as Relational Presentation.

https://www.aspirecommunications.com/video-demos/
5 short 3-5minute videos demonstrating the concept. Lots of links to free materials and additional detailed web pages.
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Building Inline Navigation
https://www.aspirecommunications.com/visual-language-tutorial-inline-navigation/
Inline Navigation features a strip of navigation at the bottom of all slides in a single PowerPoint show. A presenter, while the slide show is running, can click any link on any slide and instantly jump to a desired location. The navigation strip has one link associated with each slide. In the screenshot below, for example, notice there are only four navigation buttons. That means this slide show contains only four slides. The speaker can access any slide … from any slide.

Building Showcase Navigation
https://www.aspirecommunications.com/visual-language-tutorial-showcase-navigation/
Showcase Navigation allows a speaker to move around dynamically between all slides in a single PowerPoint slide show. The movement is always a back-and-forth jump from a dashboard slide (usually the first slide in the show, but it doesn’t have to be) to a content slide. On a dashboard such as the one shown below, for example, the speaker clicks a thumbnail of choice to access that slide. When finished talking about the content, he or she then clicks that content slide itself to return to the dashboard and make another choice.

Linking Your Content to an Existing Presentation Platform
https://www.aspirecommunications.com/visual-language-tutorial-linking-platform/
Perhaps you already have access to an existing presentation platform—such as one of the national initiatives created for the USDA or Health and Human Services departments—and now want to personalize that information with your own local data and images. That’s a great idea, but doing it the right way is important. This tutorial walks through the necessary steps. We’ll use the HHS Workplace platform as an example.
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Export Slides to Single Slide Presentations  2019 10 17
https://powerpointprogram.indezine.com/2019/10/powerpoint-vba-export-slides-to-single-slide-presentations.html
our good friend, Jamie Garroch from BrightCarbon has written some VBA code that will help you revive this option to export hundred of slides as individual slide files. Takes each non-hidden slide in a presentation and creates a single-slide presentation in the same folder as the source deck with the file name suffixed with the slide number.
C 05a PowerPoint Ribbon.docx

This may help:

If you create a custom show as Rohn suggested, then you can choose File | Save As and choose to save as PDF.  In the Save As dialog box, click OPTIONS.

In the Options dialog box, you'll be able to choose to print the entire presentation, specific slides or ... ! ... your custom show.  And if you choose that, all of the slides you've added to your custom show, and ONLY those slides will appear in the PDF.

In case it helps, you can also have multiple custom shows with different selections of slides and choose to print/PDF whichever custom show you like.