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Pablo Gallardo's Blog
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How to sign a PDF using Digital Certificate for Natural Persons in Spain

There are two methods to sign a PDF using FNMT’s Digital Certificate for Natural Persons:

  1. Using Autofirma application
  2. Digital sign from Adobe Acrobat


Methods to sign a Digital Certificate

Method 1: Using Autofirma application

Follow the instructions from this video tutorial.


Step 1: Open Autofirma application

Open Autofirma application. If you have not installed it on your computer, you can download it from here.

Step 2: Drag and drop PDF file into Autofirma

Drag and drop PDF file into the bottom part of Autofirma

Step 3: Sign PDF

Mark options like “Hacer la firma visible dentro del PDF” and “Insertar una marca visible dentro del PDF“.

Click on “Firmar fichero“.

Select the area of the document where you want to add the signature.

Select format options, like font, size, etc.

Select certificate to sign document.

Select a folder to save the signed file.



Method 2: Digital sign from Adobe Acrobat Reader

Step 1: Ensure you have the last version of Adobe Acrobat Reader installed

Latest version of Adobe Acrobat Reader application is Adobe Acrobat Reader DC.

Go to Menu Bar > Help > Check for updates to ensure Adobe Acrobat is up-to-date.

It is recommended to use Windows to avoid compatibility issues.


Step 2: Unhide the certificate functionality in Adobe Acrobat Reader DC

Open PDF file with Adobe Acrobat Reader DC.

Locate the tools pane on the right hand side. If it is hidden, go to Menu Bar > View > Show/Hide > Tools pane or press Shift + F4.

Use the search box on the top of the tools pane to look up for “Digital sign”.

Alternatively, you can also go to “More tools” in the tools pane and open “Certificates”.


Step 3: Sign the PDF document

“Certificates” bar will appear right below the menu bar. Click on “Digitally sign”, draw a rectangle in the region of the document where you want to put your signature and then select the digital certificate that is installed in your computer.

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External references

  • Unidad de Coordinación de Procesos Económicos de la Universidad Autónoma de Madrid; “Firmar un PDF con autofirma“; Universidad Autónoma de Madrid (Spanish)

About pmgallardo

I studied Computer Science at University of Salamanca. Since then, I have been working first as developer and then as SAP consutant. This blog is about problems I dealt when using computers, and more important, the solutions I found. Whenever I am on an issue and suddenlly I have a flash that leads me to a solution, I document my discoveries in a post.

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