A locked document is quite complicated to open if you have not locked it and the password is unavailable for you. You should not mix it up with the read-only access, as it allows you to preview the document, but forbid making changes in it. If file locked you can not see its content at all.
Once you received the document by messenger or electronic mail, contact the sender. The best way to get the ability to preview the file is to contact its owner and ask for the unlocking combination.
Most unlockers work only in case you provide the password. Having the proper combination you get full access to the document, removing the owner’s protection. The illegally received files are forbidden for unlocking and usage by third parties.
The protection may be removed from the PDF, using online solutions or the software. It may be the unlocker itself, like a single-function service or a poly-functional solution, that contains this tool as a part of its interface. The best way is to import and unlock the PDF using a free and secure solution, that not takes extra memory in your device. From this point of view, AltoUnlock is one of the best solutions. With it's simple and intuitive interface the process will go fast and smooth. You can easily complete it using the following steps:
Finally, you are getting a final file, available for the preview and editing from any device, that opens PDFs.