This study documents and examines watermarks found in over 44 documents from the collections of the Hellenic Literary and Historical Archive (ELIA). These documents, written between 1821 and 1829 by prominent figures of the Greek Revolution. Narrowband imaging and computational techniques are proposed for the documentation and examination of the paper substrates of these documents. This combination of techniques is suitable for documenting and examining the paper substrates of most handmade papers. The approach is user-friendly, cost-effective, and can be conducted in-situ, which is essential as historical documents cannot be removed from their storage areas due to their significance. Additionally, this methodology could support the creation of a comprehensive database for watermarks on old handmade papers. Narrowband imaging was utilized to enhance the contrast of paper texture recorded in transmitted light with a digital camera. An optical filter was positioned in front of the camera, enabling it to capture images within a narrow wavelength range of 400 nm to 570 nm. Subsequently, computational image processing was applied to improve the clarity of the watermark images. This proposed methodology allowed for the documentation and examination of all studied tasks. Out of the total number of watermarks analyzed, 78% of watermarks were recognized based on existing watermark databases. Overall, this technique produced excellent results in terms of image quality for watermarks, countermarks, chains, and laid lines.