PLEASE HELP ME: How To Keep .PDF Files From Being Modified?

[DreamingForABetterLife]

Hello everyone,

I'm new here and I really need some help... :'( 

I'm finding that I'm using ebooks more and more and these come in the .PDF format. I now have many more ebooks rather than traditional physical books. 

This is my big worry:

That the text in ebooks that are in .PDF files I have purchased and are stored on my local hard drives will be modified without my knowledge and that I would be reading .PDF files that have been modified without my knowledge and therefore learning incorrect information. I also have many .PDF files that were free and completely legal as well and I'm worried about these as well! :'(

Is there any way I can make it impossible for .PDF files to be modified/unaltered?

Any help would be greatly appreciated. :'(

[Bernd Alheit]

What kind of modification does you see?

[DreamingForABetterLife]

Bernd,

I haven't seen any modifications yet, but I just want to know how I can be sure that my .PDF files haven't been modified?

:'(

[Bernd Alheit]

Put the files on a external drive and put the drive in a safe.

[DreamingForABetterLife]

Bernd, I appreciate your reply.

I want to be able to open these .PDF files so I can't put the HDD into a safe.

How can I keep the .PDF files unmodified in terms of the .PDF files being modified by software?

[Bernd Alheit]

Then view the file only. Don't modify it.

And use backups of your files.

[Test Screen Name]

Not sure I understand where your concern is coming from. There are many bad people and bad apps, but their interest is stealing your money, blackmail etc. Rather than editing your textbooks. 

[try67]

If a file is saved on your computer then only you have access to it, unless your computer has been hacked, in which case you have bigger worries than someone modifying the contents of your text books... Why would someone even want to do that?

[DreamingForABetterLife]

Try67, I appreciate your reply.

I just want to know with 100% certainty that my .PDF files haven't been altered in the same way that I have 100% certainty that my physical books haven't been altered.

Is there a way for me to lock the .PDF files or make it impossible for them to be edited?

[Test Screen Name]

No. And what if you did manage to lock it up in this way? A bad person could make a FAKE textbook, and replace your protected file -- if you let them onto your computer, of course.

[DreamingForABetterLife]

Test Screen Name, I appreciate your reply.

Like I said, I'm finding myself buying more ebooks(.PDF files) much more than physical books.

Since I'll be storing these .PDF files on external USB HDD's, I just want to know that in the long-term my .PDF files are safe and haven't been altered and haven't been changed.

When I say "long-term" I'm thinking of multiple years.

[try67]

The only way is to digitally sign the files. If they are edited, the signature will become invalidated.

[DreamingForABetterLife]

Try67, I appreciate your reply!

I'm not familiar with "digitally signing the files"??? How does this work?

Let's say I have a completely legal and free .PDF file I have on a USB HDD: Is it possible for me to make it so that it cannot be changed forever? For example, that the .PDF file that's stored on a USB HDD cannot be changed in say, 2 years from now?

[try67]

Open the file and go to Tools - Prepare Form and then use the Add New Field tool to draw a new signature field on the first page of the file. Close Prepare Form mode and click on this field. If you don't already have a signature profile, create one and save it as a file, backed by a password. Now apply this signature profile to your signature field and make sure to tick the box that says "Lock Document", and then save the file.

The next time you open this file you would be able to validate that it hasn't been modified by right-clicking the field and selecting Validate Signature. This will work in 2 years, 5, or 50.

[DreamingForABetterLife]

Try67, I appreciate your reply!

I'm a bit confused on how your suggestion works? 

Is there another way for me to make sure my .PDF files won't be altered and will remain the same in say 6 months or 5 years from now?

[Test Screen Name]

Signing doesn't stop the file from being modified. It means you can be sure that the file has not been changed, or you can tell that it has. Unless the attacker can get access to your computer and use your signature, of course.

[try67]

As mentioned, signing is a way of making sure the file has not been tempered with. As long as the signature is valid, you know the file is the same as when it was signed and saved last. There's no way to prevent editing of a file entirely; There is a way to detect such editing.

[Test Screen Name]

Let's answer your original question directly without trying to help you solve a problem you don't actually have. You ask " Is it possible for me to make it so that it cannot be changed forever?"

The answer, now and forever is "NO you cannot do this".

[DreamingForABetterLife]

Test Screen Name, I appreciate your reply!

There must be a way for me to "lock" a file or make it so that I can see when a .PDF file was last edited???

[Bernd Alheit]

Burn the files on a DVD and hope that you can access the DVD in the future.

[DreamingForABetterLife]

Bernd Alheit, I appreciate your reply!

This is a great idea. Do you know how I could do this with other storage mediums like external USB HDD's?

[Bernd Alheit]

Sign the document with a certificate.

[jane-e]

Who do you think is going to modify PDFs on your hard drive? Have you set your computer that no one can login unless the know the password?

If you store a copy of the PDFs in another location, then you can go to File > Properties and confirm the modification date before you start reading your text books.

~ Jane