PDF files have become a very popular format and used by all Gnu / Linux users, even though it is not a very free format like djvu or epub. But its use has been so popular that more and more files are found with digital signatures or passwords that make it impossible to read these files or directly restrict some of the functions that we can perform with pdf files, such as printing or sending them. .
Here are several methods to bypass these types of restrictions or how to unprotect the pdf of passwords and limitations without having to be hackers or pay for the services of crackers.
web application
Web applications have become very popular and very accessible to everyone, thanks to the high speeds that fiber optics and the adsl connection allow. As with other tasks, we can upload a pdf file with a password and unprotect the pdf through a web application which will then return the pdf file to us totally free and with complete functionalities.
The problem with this method lies in the legal and non-computer fields. If we are going to unprotect a pdf with little legal purposes, leaving this task to a web service does not seem the best option, especially if we take into account that there is the RGPD and the request for user data. Even so, if our files are ours and we have forgotten the password, applications such as online2pdf seem like a good option.
Online2pdf would be the most popular service of all and the best of all of them since it not only unprotects the pdf file but also allows us to convert the file to any other format. A useful 2-1 for many novice users. It is not the only one, there are others that will appear if you write "unprotect pdf" in any web browser, but online2pdf is one of the best services.
Google Drive
Curiously, the Google web storage service allows us to unprotect pdf's, Google Drive allows us to do this but not as a novelty or function of the Google service but as something that has arisen as a result of other functions. In order to unprotect a pdf in Google Drive, we have to go to "New" and upload the protected pdf file to our Google cloud hard drive. Once we have uploaded the file, we right click on the file and choose the option "open with ..." and in the list that appears we select the Google Documents option.
By selecting this option, Google will convert the pdf document into a Google Docs document and we can edit, print or change certain things without having to worry about whether or not it is protected since we will use a copy of that document and then we can export it in pdf format obtaining a file that is the same but without protection. As you can see, it is a simple, fast and free option, where no one but us knows what we do or what operations we have carried out.
Use the Gnu / Linux virtual printer
This method is the best method that exists in Gnu / linux to check out a pdf file. At least it is one of the oldest methods out there. Current protection methods are not effective with Gnu / Linux distributions since Linux pdf viewers do allow the printing of these files.
In this case, to unprotect a pdf we only have to print the file and instead of doing it in a physical printer, we have to do it to a file, that is, use the virtual printer of our Gnu / Linux distribution. This new file will be pdf and we can place it wherever we want. We press the print button and the viewer will create a similar document but without the protection. A fast, simple and fully adapted to the Gnu / Linux world, we cannot do the same with other operating systems.
qpdf
Next we are going to talk about two exclusive Gnu / Linux applications that It will allow us to crack and recover the passwords of the pdf files in order to unprotect pdf in a simple way. The first one is called qpdf. Qpdf is a tool that is used through the command line or terminal and that performs a process similar to printing a protected file, that is, it creates a totally unprotected pdf file but the protected file still exists.
To use this tool, we have to install it first. So we open a terminal and write:
sudo apt-get install qpdf
We have to remember that the apt-get command has to be changed according to the gnu / linux distribution that we use.
Once installed, to unprotect the pdf we have to write the following:
qpdf --decrypt pdf-protegido.pdf pdf-desprotegido.pdf
The name "pdf-protected" is the name of the file that will change depending on the files that we want to unprotect or have protected.
pdfcrack
Generally all the above methods make a copy of the pdf file and protection is not applied to this copy. This occurs because it is difficult if not impossible to remove the protection password. But this does not mean that we cannot find out the password and be able to use it in a simple way. This function is what performs the pdfcrack program, a program that recovers the password of any pdf file in order to use it and thus use all its functions.
In order to use it, we must first install it, open a terminal and write the following:
sudo apt-get install pdfcrack
As with the qpdf tool, we must remember that the apt-get command has to be changed according to the gnu / linux distribution that we use.
Now, to use it, we just have to open the terminal and write the following:
pdfcrack -f filename.pdf -l savedstate.sav
This will create us a text file that will contain the password of the file that we have protected. A password that we can later use.
And which one do I choose?
At this point, surely you will wonder which option do I use or which do I recommend? Personally, I am not very into using protected pdf files, since if I do not want the information to spread, I better not share it. But if I have to use a tool to unprotect pdf, the one I usually use is Gnu / Linux file printing and in case it doesn't work (certain modern pdf's have outgrown this method) I lean towards tools like qpdf.
In any case we must remember that The use of these methods is your responsibility and we recommend that they be used for legal purposes or with personal files never for illegal actions. Perhaps respecting this, the best method is online2pdf. But,What method do you prefer to unprotect pdf?