PADDs were used by such space-faring organizations as Starfleet, the Andorian Imperial Guard, Bajoran Militia, Cardassian Union, Klingon Empire, Romulan Star Empire, and Vulcan High Command. They were common to cultures even as distant as the Delta Quadrant. (citation needed • edit)
General specifications Edit
Consisting of a large touchscreen display and minimalistic manual interface or control panel (generally only one or two buttons), the typical PADD was used for a variety of functions, including logging crew manifests, compiling duty rosters or diagnostic reports, entering personal data, and/or accessing library computer systems using the LCARS Interface.
Varying in size, shape and specification, PADDs were often distinguished by the species of their manufacturer or user. United Earth and Federation Starfleet PADDs were generally flat and rectangular in shape, while Klingon and Cardassian PADDs were often more angular.
Standard issue during the 22nd century, PADDs utilized by Starfleet were rectangular in shape, dominated by a large display screen taking up much of the surface area of the device. Small buttons were located just below the screen, most often grouped in two, at the lower right-hand side of the interface. Varying control button arrangements were also in use. (ENT: "Vox Sola", "Dead Stop")
These PADDs were often used to display schematics, or subspace transmissions and were capable of wireless computer networking as well as playing movies, recording logs and audio playback. (ENT: "Breaking the Ice", "Dawn", "Twilight")
At some point between 2144 and 2154, Arik Soong was able to open all the locks in a San Francisco prison he was being held at using just a PADD. After this incident, he was only allowed to use paper when sketching and writing his ideas. (ENT: "Borderland")
In 2152, a PADD was used by Captain Jonathan Archer in order to know how to arrange a series of log rings, while performing a ritual sectioning of an alvera tree as an apology to three Kreetassan chancellors outside the Hall of Diplomacy on Kreetassa. (ENT: "A Night in Sickbay")
One of the most often used devices employed by personnel serving in Starfleet, PADDs were common aboard Federation starships, space stations, and planetary facilities during the 23rd and 24th centuries.
First appearing as late as 2266 aboard such starship types as the Constitution-class, PADDs of the 2260s were large, wedge-shaped devices, operated almost exclusively through the use of a stylus. These data PADDs were often carried by yeomen aboard starships, but additionally appeared in other locations including Starfleet's Starbase 11. (TOS: "The Man Trap", "The Menagerie, Part I", "The Menagerie, Part II"; DS9: "Trials and Tribble-ations")
By 2364, PADDs had taken on a smaller profile and, while some models included one, the stylus was replaced by simple, touch-sensitive controls, typically located beneath a little, square-shaped display screen. Generally small and light-weight, the PADDs of the 2360s and 2370s were basically rectangular in shape, but varied in size, proportion, and even color – ranging from gray and muted blue colors, to red. Some PADDs, like one used by Dr. Lewis Zimmerman aboard Jupiter Station in 2376, were translucent. (TNG: "Encounter at Farpoint"; DS9: "Emissary"; VOY: "Caretaker", "Life Line", et al.) When struck with enough force, the screen of a PADD could be shattered, resulting in shards sharp enough to cut Human skin. (DS9: "Statistical Probabilities")
While the common function of these Federation PADDs was most often straight forward data entry or data retrieval, some PADDs were capable of more artistic tasks. Multiple PADDs, often larger in size than most of their counterparts, were used to draw up schematics or to create composite images or artwork. PADDs were also capable of predictive text functions, allowing users to enter a small amount of data to achieve full words or even sentences. In addition, a stylus could be used for text entry. PADDs could also order a site-to-site transport. PADDs may have been capable of sending text messages to other PADDs, based on events seen in a daydream of The Doctor's. (DS9: "Babel", "The House of Quark", "The Muse", "Image in the Sand", VOY: "Renaissance Man", "Tinker Tenor Doctor Spy")
Andorian Imperial GuardEdit
Roughly the same size as their Earth Starfleet counterparts, PADDs used by officers in the service of the Andorian Imperial Guard were rectangular in shape, highlighted by several square-shaped pieces at the sides and top which itself was rounded.
In use during the 24th century aboard Bajoran spacecraft and stations (including New Bajor and starbase Deep Space 9), Bajoran PADDs were small, roughly oval-shaped devices, nearly the same size as (though slimmer than) the small Federation PADD variant.
Capable of the same general function as their alien counterparts, Bajoran PADDs could be used to download information from primary computer sources, including text documents as large as novels. They were also able to display information in Bajoran as well as other languages. (DS9: "Emissary", "The Jem'Hadar", "Shadows and Symbols")
Consisting of a brown and gold-colored unit, the Cardassian PADD was angular and irregularly shaped, featuring an oval-shaped display screen and a number of trapezoidal and irregularly shaped buttons.
A mainstay in business dealings involving Ferengi in and outside of the Ferengi Alliance, Ferengi PADDs were often units which each had an elongated-hexagonal shape. Muted gold in color, these PADDs featured a number of button controls and a hexagon-shaped viewscreen often displaying the Ferengi interface layout, which was usually circular.
Ferengi PADDs were most often geared toward business and profit, capable of cataloging inventory, inputting vouchers, or drawing up business plans. Chief amongst their capabilities was currency transfer, allowing transactions to take place with simple thumb print verification. These PADDs were utilized by Ferengi Commerce Authority liquidators and could be found at the Tower of Commerce on Ferenginar, as well as aboard Ferengi vessels like Nunk's Marauder and at Quark's Bar, Grill, Gaming House and Holosuite Arcade on Deep Space 9. (TNG: "Firstborn"; DS9: "The Wire", "Family Business", "The Begotten", "Profit and Lace"; VOY: "Inside Man")
Both harshly angular compared to their Federation counterparts, Klingon PADDs came in hand-held and larger, landscape-style varieties. Both displaying information in Klingonese, these PADDs could be found in the chambers of the Klingon High Council on Qo'noS as well as aboard Klingon vessels such as the IKS Rotarran.
The smaller model was dark green in color and featured several button controls running up the center of the device to a rectangular-shaped display screen capable of recorded-video playback. The larger model was brown and was held horizontally with a handle attached to the left of an angular, touchscreen display. (DS9: "The House of Quark", "Blaze of Glory", "Soldiers of the Empire", "Tacking Into the Wind")
Golden-brown in color, these PADDs were roughly the same size as their counterparts from the Alpha and Beta Quadrants, but featured circular display screens with several button controls below. Among their functions, they were used to display missing persons reports. (VOY: "Workforce", "Workforce, Part II")
During the 22nd century, a silver-colored, metallic style of Tandaran PADD was available. It had a touch-sensitive screen and could be linked to retrieve information from other sources, such as from a shuttlepod and the Tandaran intelligence agency. (ENT: "Detained")
Background information Edit
The PADDs depicted from TNG onwards were conceived and designed by Rick Sternbach, who submitted the first version of the design in January 1987. He also designed the vast majority of the variations following his first version. (Star Trek: The Magazine Volume 1, Issue 3, pp. 68-71) On the PADD concept, Sternbach has noted, "The PADD was initially scaled to be about the size of a paperback book, with a larger, more comfortable screen than the tricorders, and its internal isolinear circuitry was supposed to be many thousands of times more compact than in the clipboard Kirk was used to signing. I always assumed that the PADD would be a highly capable device, able to communicate with other tech devices. The fact that we have devices like it today doesn't surprise me in the least. They're all very, very cool, but I expected them to show up eventually. The only aspect about today's gadgets that I don't think I saw coming in 1987 was how multifunction they've become. I'm not sure if I designed the PADD and tricorder and other devices to be so limited in comparison or if they were just used on screen in limited ways. You don't see people talking into a PADD or a tricorder, though there's no good reason why they couldn't have." 
As foreseen by Rick Sternbach, not long after their debut in TNG, PADD-like devices became indeed a real-world technology with the introduction of personal digital assistants (PDAs). Since then, devices with touch-sensitive displays and user input systems which reconfigure themselves depending on the task at hand have become common, the most notable one being Apple's iPad, introduced to the general public on 27 January 2010 by CEO Steve Jobs. The iPad carries a name that sounds suspiciously like that of the fictional Star Trek device, a circumstance not lost on others, including Star Trek actor Brent Spiner.  Sternbach himself took a more laid-back position on the similarities issue, having stated in October 2011, "I can understand why there's been some hoopla over the comparison to recent tablet computers, particularly the Apple iPad, but I really see the PADD as simply an outgrowth of science fiction data displays imagined for decades in literature and on screen."  Contrary to competitor Bill Gates (having done so for the personal computer in the documentary How William Shatner Changed the World), Jobs never acknowledged Star Trek as a possible source of inspiration.
Unlike their real world counterparts, most PADDs on TNG, DS9 and VOY were nonfunctional, rarely even incorporating lighted display screens, but rather printed "okudagrams". Lighted PADDs did eventually make their way to screens for Star Trek: Insurrection, with custom and store-bought devices like the Cabin Light Box being used through Star Trek: First Contact and into Enterprise.
A Risan PADD used by Freebus appears in a deleted scene from ENT: "Two Days and Two Nights". From the device, he sees that Enterprise crew members who have decided to visit Risa on shore leave have selected "a wide variety of locales and activities." However, he also sees from the PADD that T'Pol has decided not to go with them.